A dog should be crated at night if the dog cannot be trusted to not get into things at night.
Some dogs are okay not being crated at night and will sleep in their own bed or sleep in the same bed as you.
In that case there's no need to crate the dog at night as long as it's good at night and won't get into things or tear things apart such as furniture etc.
Some dogs also when in the puppy stage or when they are into tearing things up will need to be crated at night or when left alone for awhile.
But you should not leave a dog crated alone for longer than 8 to 10 hours.
If you have to be gone longer than a few days then take the dog to a dog sitter or kennel where they can watch your dog for you.
Or if possible take the dog with you.