Hi, Tracy -
I've worked on several PFC-based applications over the last 25+ years, some internal-use only and some commercial, ranging in size from moderate to quite large -- all of them making fairly extensive use of the tab control.
I've rarely, if ever, seen the u_tab and u_tabpg objects used. The PFC does a very good job of recursively identifying all of the updateable objects (DW's, ostensibly) that are contained within the non-PFC-based tab pages of a non-PFC-based tab control for retrieval and updating via the Linkage service and Logical Unit-of-Work service, even when a tab page contains a "nested", secondary tab control that contains several tab pages.
The ancestor pfc_u_tabpg object is an empty "placeholder" object... it contains no code or properties, so there's no real functionality being added by using it.
One benefit of using the u_tab object is it helps you to implement a user-interface that is a little easier to update, whenever (or if) your GUI standards change, but IMHO that has not a major selling/benefit point in the applications I've worked over the years.
I'll be curious to learn what others in the Community have to say on this topic
HTH, John