We started using the sock buddy because he was not just plucking his feathers, but actually starting to chew little holes in his skin
I came home one day to a blood smeared cage, and that was it- on went the sock! Even when he is not wearing it now, he does not do that, but he does shiver alot without it so I do think it helps keep him warm also.
Alot of people use it to stop plucking, and I think it does help with plucking to some degree because they can chew on the sock instead of themselves- it's like a toy they are wearing all the time
. I think the idea is that it is supposed to stop plucking by blocking their access to the feathers, but my experience has been that he can get right underneath it and pull the feathers no problem (he can even pull a feather up through the fabric of the sock, now that takes dedication!). Maybe if it was tighter he wouldn't be able to, or if the slit for his wings and feet were 2 separate holes so the side wasn't all the way open, then maybe it would prevent the plucking as well.
To change it, I cut off the old one and then put on a new one, probably every 1-2 weeks, depends on how wet he gets in his shower every day. Most of the time he just gets a little damp from the moisture in the shower, but once every week or two he decides to take a real good shower (I can tell that he wants one if he starts spreading his wings and dancing in the shower, then I move him where he can get right in the water)- once it gets soaked, I change it (I usually hop out of the shower and remove the old one as soon as I see he wants a good shower, that way his skin under the sock can get all clean too!).
I don't think a fully feathered bird would need it at all, I think if they were outside in the winter and it was cold enough to be a concern, the sock would not provide enough warmth to be of much use... But I don't really know. Greenbean is really calm about getting his on and off, but I have read of plenty of birds that get really stressed and upset by it, so probably not worth doing unless there is a real need for it. I don't think little birdie outfits are going to take-off anytime soon, although they are quite cute