The only trouble that I found when using these positions was that the original jaw, when moved to position "B" in the alternate page to which Jason refers, is that there is very little meat for the jaw to grip with. I get around that by using some slightly longer screws and a couple of parallels as shown below:
This gives a much larger area above the fixed jaw, However, I would caution against use in this way except as a quick-and-dirty fix. I must admit, having said that, that I have used it to hold a rotary table in the vice for a one-off job that would have otherwise have needed a swap-out and subsequent re-tramming of the vice. It does, of course, assume that headroom is sufficient when used this way.
It has also allowed the fixture of plate material for machining while held in the the vice that would otherwise be too large to fit between the jaws in normal use.
A similar set-up on thee moveable jaw extends the scope of the vice accordingly.
John