there is a difference in what the dog gets out of it and what motivates the dog . . . one of the guys i've trained with reminded me recently that while a lot of dogs, such as herders, are into the "winning" aspect of bitework (subduing the bad guy, taking control of the situation and ending up on top), a lot of pit bulls are into it for the fight and may well look at a prolonged fight with the bad guy as the reward itself and may well lose interest if they start to win too easily.
so when you're building a dog up, some dogs are going to need lots of positive associations . . . for some dogs, that's going to mean a lot of "wins" and slipping them the sleeve a lot to give them that sense that they've accomplished their goal. you may see a lot of dogs run a circle with the sleeve in their mouths, they look quite proud and satisfied.
for others (like my dog), there isn't a whole lot of joy in the "win" itself because it means the fight is done . . . he'll "win" the sleeve but he won't run a circle with it and feel like he's got one over on someone. he shakes the sleeve and tries to engage it some more, realizes that it won't fight back, then goes right back to the helper to try to engage in more fighting . . . .
of course, not every dog is the same, and some shepherds or herders will want to go back for more and some pit bulls will be over the moon about simply winning that sleeve. but i think if you look at bull breeds in general, a lot of them get a lot of pleasant adrenaline and stimulation from the fight itself and someone working those dogs needs to be aware of that . . .