How to assign different functions to responsibilities

My business users need to open varoius responsibilities for their daily tasks they do on R12. For example, a person woeking with MFG may need to see a form in PO and another in OM as well. So, the users have to toggle between different responsibilities frequently. For convenience, these users keep multiple seesions open on their PCs for getting tasks done without hampering any activity.
This (keeping of multiple sessions open) may hamper the Performance of the system.

Hope I am able to desribe my concern.

Please revert, if I can design individual responsibilities (like user wise responsibilities) wherin I can give access to all the forms required by the user through the single responsibility. Do let me know if there is a document available describing the setups.