A preexisting problem such as aggression or timidity may intensify in response to the dog's frustration at being crated excessively. Used properly, however, a crate serves as your dog's den, providing security and comfort in your absence. If you are confining your dog to a crate or a safe room until he learns the house rules, you or another family member should come home during the lunch hour if at all possible to provide social contact, fresh water, and the opportunity to eliminate. If this is not feasible, enlist the aid of a pet sitter, friend, or neighbor, at least initially. No dog should be crated throughout the day and again at night.
Puppies require special crating procedures.
Finally, be prepared to exercise your dog as soon as you arrive home. Whether he has been confined in your absence or has had free run of the house, you can't expect him to wait patiently after you get home from work while you put your feet up and read the paper. He has been coping with social deprivation all day and deserves your full attention as soon as you arrive. Of course you can't quit your job and put your life on hold to stay home with your dog, but with planning, preventative training, and proper confinement, you can make those unavoidable periods of social isolation much less stressful for him.