"Bob La Londe" fired this volley in newsxiJr.46524$l_
:

Ok, I just don't see the purpose. It's a freaking swivel base. Why?

Keeps the vise in a known position on the rotary base, so the fixed jaw is
always at a certain radius from center.

I'm not sure I do it, but I can see its usefulness, especially if one were
doing a lot of one particular part (not in batches) over several changes of
tooling and fixturing.

LLoyd