I've been using a full bodied whitetail decoy for years. I think it is a Feather-lite. It's bulky to carry, noisy to set up, and a whole lota fun! Half the archery hunters in my office are now using them, and between us, we've just about seen it all.
The best use for the decoy is bringing bucks from way out there in an open field, and positioning them right in front of you. We have only been successful setting the decoy as a buck. Set as a buck, the decoy must face your position as precisely as you can set it. Bucks come in to face the decoy, but they often get nervous as the decoy just stares at them. If you are hunting from the ground, you must be a minimum of 35 yards from the decoy. Even that is probably not far enough. On the ground, you can not get away with hardly any movement. You can do gymnastics in a treestand without scaring some of the smaller bucks that come to the decoy.
None of us has ever decoyed the same buck twice, so make the first time count. One of the guys carries rocks to throw at the little bucks to get rid of them, before the big guys come out. Another guy had a little 5 point run right through the decoy, knocking it apart. I had a button buck stick its nose right up under the decoys tail, and didn't like what it smelled!
If you have a good set-up where the decoy doesn't add anything don't use it until you feel you need some extra help. If the decoy adds something to your setup, take it out on the first day. For all the fun we've had none of us has yet killed a BIG buck over the decoy.