That is why you practice them. Even if you are good in other areas, then doesn't mean you should just neglect your weaker aspects. They are a vital part of the game and could be a difference in drawing games or winning them. Someone could easily score an OG from it! You don't have to be in form to put in quality crosses. Even when Ivanovic was, he hardly put a good one in. And tell me, when was the last time Ivanovic put in a really great cross?