I think it depends on the situation and there are valid reasons, but unless your bird is going thru crazy hormones (or not) and dive bombing and its coming down to a matter of personal safety or safety for the bird, then its not really something good for the bird.
I recently saw a post here about bringing your bird around your house and letting him feel all the windows and walls and things that may get in his way, so that he knows not to fly into them, kind of like a tactile recon of the place before letting him loose.. sounds like a good idea regarding concern for injury related to flying into thing.
Personally I do not like clipping wings. I have a sun and he has free roam of my apartment all day. When hes ready to sleep he goes to his cage and into his bed by himself but i rarely ever close the cage door unless he is being real bad. Now im not saying that everyone should do this but i just personally feel better knowing that he can excersize and fly and play on his hanging "gym" while im gone. Make sure the place is safe though!
I know that a "no cage" policy is not possible for all but I think that at least allowing the bird flight when allowed out is crucial. The breeder I got my sun from clipped his wings and I never did after that, and I literally saw a change in him. His confidence and happiness, and especially independance have all changed and/or developed for the better. Its like giving a paraplegic legs that function IMO.
When a bird can fly, naturally it is going to be less dependant on you, but also feel safer knowing it can easily get out of a situation it comes into. I bring this up because training is important with flighted bird IMO. By this i mean, for one, that you build a trusting bond with him or her and also in the sense that your bird listens to you. For example you shouldnt have to run around your house ten times to "catch" him or her for whatever reason. Thats a whole different topic though.
I got kind of sidetracked but one of my points is that I think a bond with a bird who is fully flighted is a special bond in the way that the bird is choosing to leave his toy or whatever he is doing to come be with you, while at the same time you and him or her both know that when he feels like doing something else, he can do it on his own.
Some people might like that a clipped bird is dependant upon them, but personally I think that is selfish, and find it much more rewarding when the bird wants you, not "needs" you.
Like i said, there are some situations where clipping is for the benefit of the bird so I am not taking shots at anyone who has their buddy clipped.
She has made an attempt or two when she has been spooked,only to land with a "thud" a foot or two away from where she was.
