When I bought my car it had a wind deflector in it. I drove home 2 hours at about 75mph with the top down and it rattled the whole way home, so I ripped it out.
Just a couple of weeks ago, I found that some of the plastic silencers were out of place and some were missing. So I fixed them and I put it back in.
No rattles, but I really don't notice a difference with it in or out. The only cool thing is that you can put a sign or logo on the plastic ones.