Project Permissions 
The Project Tools include an extensive permission system that ties into vBulletin's existing usergroup system. Permissions are definable for all usergroups on a per project and per issue type basis.

The following standard usergroup permission concepts apply to the Project Tools:

Project Tools permissions are definable at a global and per-project level. If you do not define any permissions for a specific project, the global permissions will apply.

Multiple Group Membership
Like in the usergroup system, if a user belongs to multiple groups, the most permissive value for a specific permission will be used. That is, a yes will always override a no. This is a useful way to apply specific project permissions to certain users in a group.
User Contributed Notes: Project Permissions