Where you should put your puppy depends very much on your individual circumstances.
Crate training, however, is a very good housetraining tool. It is
only a tool though - not a permanent way of life, and that should not be forgotten
The reason crates are useful in housetraining a puppy is that they provide a strong incentive for the puppy not to potty inside. When he is not in his crate, you are constantly watching him and you take him outdoors when he needs/will need to potty. And when you cannot be watching him, he is in his crate - where he will not potty unless he absolutely has to (and if that happens, it means you left him too long).
BUT: There are limits to any dog's ability to hold their bladder. For a baby pup, he might be able to hold on for three hours in the crate without
having to potty. But he will not be capable under any circumstances of holding on for 6 hours. So if you have to leave a baby puppy alone for that long, then a crate is not a suitable place to leave him. You must always provide adequate toileting opportunities if you wish to housetrain a dog - and like I said before, the crate is a training tool only.
Anyway - if you are home all day with your puppy and want to use a crate for the times you can't watch him, then it will be a very useful training tool for you. And if you work, but are able to come home to let your puppy out at regular intervals (or can get/pay someone to do it for you), then it is still a good training tool. But if you need to leave your puppy alone for extended periods, and can't give him a break and a potty stop during the day, then you should NOT leave your puppy in a crate. In that instance, gating him in your kitchen or bathroom with some newspaper is a much better way to go. There is no way a baby puppy could possibly hold his bladder all day long - and forcing him to sit in it is just inhumane.
Does that answer your questions? Really, whether or not a crate is a suitable place for your puppy during the daytime depends entirely on your individual circumstances.
Incidentally, the length of time an average puppy can hold their bladder during the daytime is (in hours) the age in months + 1 to a maximum of 8 hours. So that is 3 hours for a two month old pup, 4 hours for a three month old, etc. However - please remember that that is the limit of physical endurance we're talking about, well beyond the stage his bladder became uncomfortable. If you do not
have to leave your puppy without a potty break for the maximum time he can possibly hold on, then don't. It will not be particularly pleasant for him
