[rtrombone]

vehn is only partly right. As you mentioned in your post, Diplomat, it's impossible to know with absolute certainty what your opponents hold. They may be going for low, high, both, or, on Party, neither [img]/images/graemlins/laugh.gif[/img]. The hands people have turned over...you're convinced they were going low all along, and instead they've got a full house!

So a raiser on 7th street may think he has a lock on the low and has put both his opponents on high hands, or vice versa. He raises for value. Alternatively, he may have a not-so-great high hand and put the bettor on a low. He's not sure what you have. He raises in an effort to force you to fold a hand like two small pair. (Maybe you were going for low and backed into them.) Yet another possibility is that he has a mediocre low and puts the bettor on a high hand. He raises if there's a chance you'll fold a bettor low that you've backed into. And if you call with another high hand, that's fine, too. You get the idea.

Because of the exposed cards in stud, you can represent a bunch of hands even though the last card is dealt face-down.

This aspect of river play also exists in regular stud, but to a much lesser extent. There, a guy may try it if he suspects the bettor is representing a much stronger hand than he actually holds, but doesn't think he has you beat. He raises in an attempt to win the pot with the second-best hand. The same goes for hold 'em. It's mostly a stud/8 thing, though. I suppose it can come up in omaha hi/lo, but not as often, because of the possibility of being quartered.