Yes.
Yes, major---especially for hatchlings/young tortoise.
It is to assure your tortoise remains hydrated, which lends to keeping your tortoise healthy.
It is to keep them hydrated. During the first 10 minutes of the soak a tortoise will put their whole head underwater and drink. It is very important to soak babies as dehydration will kill them. If you have one that drinks on his own from a water dish in his habitat soaking is not imperative. But hydration is the key to healthy living and most torts when young don't drink on their own. We keep them on slow cook under hot lights so soaking is pretty important...