HI,
My suggestion is to develop function of having possibility of > one user to be able to use more security levels!!!.
To explain a bit more: as I developing different modules in one mini ERP project, It is quite difficult to manage all option at user level. For example: level A covers 3 modules (3 sets of tables, e.g. timesheet, purchasing and tasks) and having 25 users on this level. Now, one of the users is not to be allowed for purchasing any more, therefore I would have to create new security level with two sets of tables just for him. As organization grows, thus the complexity is as well.
Instead, it would be better to have three groups of tables (levels, modules) and then just to assign some groups to an user who can then use functionalities of all assigned groups, combined.
Davor