Hm, I think it could be great to have workshops of different sizes, for instance...
1/ Small Workshop (current size)
Needs : 1 material to build.
Size : 3*3
Workers : Can be used by 1 dwarf at the time.
Clutter : Get cluttered with 15 large items, max clutter at 55.
2/ Medium Workshop
Needs : 3 materials to build.
Size : 5*5
Workers : Can be used by 2 dwarf at the time.
Clutter : Get cluttered with 30 large items, max clutter at 100.
3/ Large Workshop
Needs : 10 materials to build.
Size : 9*9
Workers : Can be used by 5 dwarf at the time.
Clutter : Get cluttered with 100 large items, max clutter at 300.
It can help to get rid of more excessive stone, economize fortress space, resolve clutter problems in workshops like Butcher's worskop or Kitchen, etc...
Multiple workers at the same time will work on different tasks in the workshop's joblist (which could be expanded in larger workshop).
In a Medium Glass furnace for instance, one dwarf could make raw green glass while another collect sand. Idem with a Medium Loom : One could collect webs and his workmate weave them into silk.
Of course the values I set (the sizes, materials to build, clutter limits etc...) are just for example.
Yes ? No ? Ask if there's something unclear (because as you may have understand, english is not my mother tongue...).