1. To housetrain. The easiest, surest way to housetrain your pup is with a well-sized crate. A crate with a divider for large dogs is perfect for puppy's space to grow with him.
2. To give your dog a safe space. Sometimes our household gets stressful for even the most stable dog, and a crate is something that's just his and stays the same no matter what! If you're moving homes, hosting houseguests, going to a dog sports trial, or even just going to a hotel, your dog has his own "room" that he feels safe and relaxed inside.
3. To protect your dog from himself. Even good dogs have bad days. My personal favorite example is my old doberman, Dazz. The best dog ever, loose in the house since she was 2 years old and housebroken, at 13 started needed prednisone. Pred is a steroid and stimulates appetite. You can imagine the destruction a dog can wreak on an apartment in 6 hours when they're absolutely convinced they are starving. She found things even I didn't expect were edible (or even palatable!) Always remember, your dog might be an angel, but even good dogs may have to go on appetite-stimulating drugs!
4. To make the vet less stressful. If this is the only reason you decide to maintain a crate behavior, this will be worth it. In case your dog has to stay overnight at the vet for some reason, being used to a crate will make it way less stressful. There are many other reasons that would require your dog being crated besides the vet, as well - flights and quarantine if you're traveling internationally, evacuations in the event of an emergency, boarding in a kennel etc. Some of these may be worst-case scenarios, but a well-trained crate behavior will make the ordeal much easier on your dog.
5. To train other things. A crate can be a fun exercise to teach behaviors! A few examples: sending your dog into his crate at speed from anywhere in the house, waiting with the door open until you give him the release word, even a good retrieve his toys into his crate. Have fun with crate training!