"Because I said so" - is that really fair? Do you say it?

The only time I used "because I said so" is when there wasn't time to explain but my kids always knew I would explain later. I don't believe a plain old "because I'm the Mom" or "because I said so" is fair at all and it doesn't teach the kids anything. If you look up the word "discipline" you'll find out it means to teach/learn. That's what parenting is all about-- teaching. To teach people to use good judgment themselves you have to be able to explain your decisions. At the same time I feel it is important to teach kids a respect for authority while caring about the details.