Dog crates, also called a den or a cage are extremely useful.

A good quality crate provides a secure den during a dog's integration period in a new home, and makes the introduction of him to existing pets more manageable and less traumatic.  When you can not be around to supervise young puppies, putting them into the crate will keep them safely away from wires and other hazards that could cause them harm and prevent then from doing harm.  Once a dog is no longer a puppy, his carte often becomes his personal space of choice for naps.  

A crate is very useful not only for home but for travel as well.  Many of the wire crates are foldable, the soft sided crates are light as well.   Many dog owners have a crate for their home and one that is kept in the car to keep their dog safe during travel.