My trainer has trained many police dogs who have excellent street bite records and does 2 things that contradict what Andres said... 1) He uses sleeves for all the grip work until the dog is ready for suit and muzzle work, 2) Dogs win the sleeve as a prize and carry it.
There is lots of civil agitation when we work dogs, we'll toss the sleeve in one direction n continue to agitate the dog, if the dog chases after the sleeve then sting the dog in the butt with a whip n he'll quickly realize that the man is where his focus needs to be... it doesn't take more than 3 minutes to make a dog realize this, provided you have done civil work with the dog from the beginning. People get very weary of doing "defensive work" with a puppy, but if a dogs temprement can handle it, throw in some "challenges" while doing prey work, very quick, maybe 1 or 2 seconds, you're not threatening to kill the dog, but you're building a foundation to get the dog focused on the man later in their work. We have some very nice dogs at training who, if you were to slip the sleeve, they will spit the sleeve and come back at you... then we have other dogs who you can slip the sleeve and they will run around happily with it in their mouth, but they have bitten people for real.
My general philsophy is "there's more than one way to skin a cat"... dogs can see a bite suit as equipment too, but they never learn a proper grip if all they do is suit work... some people will argue that grip is only important for sport.... I agree with this to a certain extent, but a dog nipping at the end of the suit instead of jamming their mouth over the whole arm is gonna end up biting a suspects jeans or t-shirt in a real life apprehension, the full or 2/3 mouth bite is important to make sure someone really gets bitten, a dog hanging onto clothing is as useless as not having a dog.
Whatever works for you or your trainer is fine, but I wouldn't say there is only one way to do it, because it's been proven time and time again that there's more than one way
Some dogs are just equipment oriented, they seek comfort in the equipment and don't understand the concept of biting a real person, other dogs have no problem transitioning from sleeve work to civil work and couldn't care less what they bite, as long as they bite something.