Clipping is done for two reasons: 1) to keep the bird calmer and in a lower
place in the pecking order and 2) for the birds safety. If the bird can fly away anytime
you are using some sort of control (step up command or whatever) then the cockatiel is at
the top of the pecking order and you should always be at the top.

The biggest reason is safety. Bird don't see glass or mirrors and when they fly at these it
usually ends up with a bird with a broken neck. They can fly out the door, window, into a
toilet, a boiling pot of water the list can go on. So, Yes, I always recommend that the wings
stay clipped.

Kathy Greaser
http://members.tripod.com/~KGKAT/Aviary.html