[rdl]

Baggage handlers at airports pull bags off the belts and put them in a line nearby (and sometimes give them to passengers) when there's a need to clear the belt, or when they don't have other work to do (at some airports). This is mainly to keep the belt from filling up.

They also sometimes do this when looking for a bag for transfer (which failed to get interlined correctly or something, or when an elite has a connection but there's no interline agreement.)

[therein]

I am sure these people attend other tasks once that's done. They likely also have other belt-related tasks to deal with behind the doors.