Sometimes I think that crates are used purely because new owners think it’s the ‘done thing’ and too often puppies are just put into the crate and expected to be ok. I crate train. The main reason is for transportation. For 90% of the time, I expect my puppy to choose to take herself into her crate and have no reason to shut it. Some advantages of a crate are that it provides a clear boundary for people so that it is harder to disturb a sleeping dog; it can create a cosy dark cave; some puppies and dogs prefer a small enclosed space; it can help teach an ‘off-switch’; it can be a safe space when staying somewhere unfamiliar; if introduced properly it prepares for inevitable confinement (transportation, vet stays, crate rest etc)… I am sure there are other advantages.
However, if the puppy/dog does not choose to use the crate and/or shows any distress when the door does have to be shut, more crate training needs to be done and in the meantime the crate should not be closed. My preference in the home is to puppy-proof rooms the puppy has access to, rather than confining the puppy to a crate when unsupervised. The crate is just one option of many resting areas within these rooms.
A real-time 4 min video taken the first time I did some crate training with my 8 week old puppy. It is not always this textbook, but if you are starting from scratch with no previous negative associations with a crate or confinement, it should be relatively straightforward…