A large number of breeders over here band their birds... my P'let hasn't had any trouble with his...closed or open bands, maybe I'd not choose to do this, but my 2 birds were banded when very young by the breeder...
I'm going to contact the breeder to see why she does it....
Will get back to this topic once I hear..

Had an answer from my breeder...
its done in the UK for tracing back to the breeder, also for sexing the bird...
the open split ring or closed, is a preference to the person breeding...

I don't band my babies because it seems to me that the potential risks outweigh the potential benefits. I've heard of parent-raised babies being injured because the parent tried to remove the band. Which is a perfectly natural reaction from the parents because they know that metal thing doesn't belong on their baby's leg.

If I was a show breeder I would have to do it though, because bands are required to compete at a serious level. The organizations who put on the shows want to be able to ID the birds. I'm not sure why they want this, but competition can get nasty sometimes and if nothing else this would prevent arguments about whether a particular bird had been stolen from someone else.