I would only use them if they are required for shows or you need them for support on the legs if you are doing a harder workout than normal. If your horse wears them all the time then it can potentially weaken the tendons and ligaments as they become dependent on the support from the wrap.
It depends on what displine you do. If you jump you should wear polos in the back and boots in the front. If you ride western you should have wraps for barrel racing/reining and polos for hack classes.
Why do you feel you might need to? Depending on that answer it will tell me what type of wrap you are thinking of needing( standing, polo, sweat etc.) and depending on what wrap you are thinking of I can tell you the circumstances I would use them for :)