From Online Manual
SMF enables you to have separate permission profiles for each board, so that membergroups can do different things on different boards. Permission profiles only contain board-related permissions. You can assign whichever permission profile you want to each of your boards. The "default" permission profile is assigned to boards that do not have a custom permission profile.
With permission profiles you can, for example, allow a membergroup to post on one board, but not on another one - simply assign different permission profiles to these two boards. Or you might want to allow users to reply to posts, but not to create new topics in a certain board - this can also be done by assigning a permission profile to the board. If you want any other boards to have the same set of membergroup permissions, then you can assign the same permission profile to those boards as well.
Creating and Assigning Permission Profiles
Permission profiles can be created, edited, renamed and deleted in the "Edit Profiles" section of the Admin Center (Admin > Permissions > Edit Profiles). Note that permission profiles can only be renamed or deleted if they are not currently assigned to a board.
Once you have created a permission profile, you can assign it to one or multiple boards on the "Board Permissions" page (Admin > Permissions > Board Permissions). When you click on the name of a board, you are taken to its configuration page where you can select the permission profile that it uses.
Examples of Permission Profiles in Practice
Here are two examples of how permission profiles can be useful for your forum.
Restrict Where New Members Can Make Their First Post
One permission profile that administrators often like to create is one which limits which boards new members can post in until they have made their first post. The following steps give an example of how to create and use such a permission profile:
- Create a Post Count Group
- a) Go to Admin > Members > Membergroups > Add Membergroup.
- b) Create a new post count group that requires, for example, one post for membership. Enter the name of the group in Membergroup name ("1 Post Group", for example). For Group Type, select "Post Based". Enter "1" in the Required Posts field. In the section Permissions, select "based off of" and "Regular Members" in the dropdown list. You can check all the "Visible Boards". Click "Add Group", which takes you to a further configuration page.
- c) On the next page you can configure a few more aspects to the new group. You might not need to change anything and so simply click on Save.
- Enable Permissions for Post Count Based Groups
- Make sure this option is enabled in Admin > Members > Permissions > Settings.
- Change Permissions for the "Default" Permission Profile
- a) Go to Admin > Permissions > General Permissions.
- b) Click on Modify next to "Regular Members" and make sure that all posting permissions are unchecked.
- c) If your zero-post group (called "Newbie" by default) has permissions assigned to it in the default profile, you must make sure that it has all posting permissions unchecked.
- d) Click on Modify next to "1 Post Group" (the name of the post count group requiring one post) and make sure that all posting permissions are CHECKED.
- e) If you have any other post-count membergroups that require more than one post, you must make sure that they have posting permissions CHECKED. For example, the default "Jr. Member" post count group requires 50 posts.
- Create a New Permission Profile
- This permission profile will be used for permitting users with zero posts to make their first post in the board(s) to which it is assigned.
- a) Go to Admin > Permissions > Edit Profiles.
- b) At the bottom of the page, create a new profile, named for example "Zero Post Group allowed to post". In the field "Copy Permissions From", leave it as "default". Click on "Create".
- Change Permissions in the New Permission Profile
- a) Return to the Edit Profiles page (as in the previous step) and click on the name of the new permission profile that you created. This will enable you to change the permissions associated with this profile.
- b) Click on Modify next to "Regular Members". Scroll down the page and make sure "Post topics and replies to the board" is CHECKED. Click Save Changes at the bottom of the page.
- c) If you have enabled the option to deny permissions on your forum, make sure that the zero-post group (called "Newbie" by default) has not been denied permission to post topics and replies.
- Assign the Permission Profile to the Board(s)
- a) Go to Admin > Permissions > Board Permissions.
- b) Find the board where you want members with zero posts to be able to make their first post. Click on the name of this board and you are taken to a page to modify this specific board. The only thing you need to change is the option Permission Profile - in the dropdown list, select the new permission profile that you created ("Zero Post group allowed to post"). Click on Modify at the bottom of the page in order to save this change. You can apply the same permission profile to multiple boards.
After you have completed the steps above, users in a post-count group with one post or more will be able to create new topics and reply to topics in all boards, but members that have zero posts will only be able to make their first post in the board(s) that have the new permission profile assigned to it.
Enforce Post Moderation Only For New Members
The following instructions demonstrate how you can use permission profiles to ensure that new users with up to and including five posts are moderated, but regular users with more than five posts are not.
There are, in fact, two ways to do this, indicated as path A and path B:
- Turn on post moderation in Core Features.
- Making sure that the zero-post count group is left alone, create a new post count group that requires 5 posts, so that once a user has successfully posted 5 posts (and until they're approved, it won't affect their post count), they can have different permissions attached.
- Go to Admin > Members > Permissions > Settings and tick the option "Enable permissions for post count based groups". Click Save.
This is where the paths diverge. Here's path A:
- A4. On the same page as above (Admin > Members > Permissions > Settings) also tick the option "Enable the option to deny permissions".
- A5. Go to Admin > Members > Permissions > Board Permissions and for each permission profile (that allows posting) set the permissions up as follows: Regular members should have "Post new topics, without requiring approval" and "Post replies to topics, without requiring approval" enabled, while the zero-post count group should have those permissions *denied* and "Post new topics, but hide until approved" and "Post replies to topics, but hide until approved" in their place. Once the user leaves the zero-post count group for the 5-post count group, the other permissions are no longer denied. 
Alternatively, you can follow path B. This path doesn't require Deny permissions:
- B4. Go to Admin > Members > Permissions > Board Permissions. For Regular Members, set all the posting permissions to Disallow. Then in the zero-post count group, give them "Post new topics, but hide until approved" and "Post replies to topics, but hide until approved" and for every other post count group, give them "Post new topics, without requiring approval" and "Post replies to topics, without requiring approval". 
 In this case, we have an extra membergroup that does absolutely nothing other than allow another group's permissions to expire.
 This means you still have the extra group, but at least the extra group is now doing something. This is also very fractionally faster, but harder to maintain as you have to set the new permission up on any new post count group you create.