Pet Bird Flying Around the House?

If you have a pet bird, do you let it out of the cage sometimes to just fly freely around the house? I've never had a bird (but always wish I did when I go into PetSmart and see some of the totally beautiful birds they have!)

The reason I'm asking is because I've had two different friends who did that... just let the birds fly free (both parakeets) and every time they mentioned doing that, I always wondered if it was a good idea. Never having had a bird, I didn't know if that's just something people always do or if it was unusual. My thought was always that it didn't seem very safe but... ???

I think what I'd do is let the bird out to interact with me, but most likely in an enclosed room where it couldn't fly free over the whole house, hide, take a risk of someone opening an outside door, etc.