I steady them to wind and shot because I field trial and hunt test. A couple of arguments for steadying your dog are:
1. You don't have to worry about him chasing low flyers and not giving you a shot, or you taking an unsafe shot and hitting the dog.
2. The dog chases a missed bird (or a hen), doesn't recall and flushes more birds out of range.
The main argument I have heard for not steadying is the dog will get to the fall faster and you won't use as many runners (However, IMO most steady dogs are really good markers and will not loose many birds either)