I've used up to 8 at a time thus far Very handy if you've got lots of vises on the table of a mill.
But for lathe, I can imagine that some guys might have a series of parts that they run over and over. If the parts have a different chucked length, then they need a different work offset for each program. Some of us might just go in and modify the G54 for each job, but you don't have to. You can set up a "permanent list" of offsets, and dedicate them to particular programs which work at that part length, and if the program calls the corresponding work offset, then you never have to edit the offset table at the machine. It could be more trouble free in well controlled circumstances, than forgetting to recheck the G54 after loading in a new program.