Have you ever tried to bathe your Bull Terrier and while you were trying to wash off his belly he kept sitting or laying down? As a Bull Terrier, your guy is probably heavy, and a wet, slippy, and heavy dog is not something that you want to be lifting over and over again, especially while you strain over a tub. What about when you brush him or the vet needs to look over him--same problem right? Perhaps your guy or girl is a beautiful show dog and sitting during inspection is just not OK.
Having a dog that knows how to stand when told to can be very helpful and, at times, even essential. Whether your dog is fine with being touched, needs to be lured, or responds best to learning on the go, there are a lot of ways to teach your dog how to do this fairly simple command. Once your dog knows how to stand you can also teach him how to stay in that position, and that can really come in handy.