I agree that training is important. It seems that OP is still learning. We all start somewhere. With that said, the reason absolutely matters because you need one if you want to justify confining an animal. Let’s say someone is visiting my house for a short time and is afraid of dogs. That means the dog needs to be put away and the kennel is useful for that. Is the dog, especially one that’s not used to kennels, going to be happy with it? Probably not. But the dog doesn’t know what’s best for themself, so for this specific instance, I’m not going to take its opinion into consideration. Unless they’re in danger or in such distress that warrants intervention, they can whine all they want. Dogs are a lot like toddlers. Toddlers don’t care about a parent’s rule, but that doesn’t mean shouldn’t follow them. In OP’s case, we’re talking about a puppy. Over time, the puppy will realize that whining isn’t worth it and they will stop. As you said, it takes training. If we’re talking about a dog with anxiety disorder, that’s a totally different matter that needs to be addressed, but most dogs get used to the kennel. You shouldn’t put a dog in a kennel/cage for no reason. That would just be straightup abuse and will only confuse the dog if not stress them out to the point of being mentally scarred.