First; this is not to ask for a step-by-step training advice.
There are many questions and answers on Pets-SE that mention "crating" and "crate-training" a dog. First time I personally found crate-training was in this question:
Having my doubts I went to Google it, to find "How to Crate Train your dog or puppy." which I read until this "Never close the door until the dog is relaxed and comfortable." came up. Of course I read the rest of the article too, but that quote is what made me ask this.
Okay, we had a crate for our dog too. The crate was there for the dog to go in to have a peaceful place to sleep and rest. Here's the difference, we never closed the door. At the moment we don't have any crate at home, except those disassembled ones in basement. I consider both of our dogs "crate-trained" so that they feel okay in a closed crate when we take them to a dog show. Maybe we are just lucky to have two such nice dogs that we can leave them home by themselves while the human members of our family are away at work and school.
So, the question. Why would I close the crate door at home? What is "crating a dog" really? What purpose has it, other than to offer a dog a safe place to sleep and rest?