I have seen decoys both help and hurt the hunt...
If I am hunting in the woods, I think there is an advantage to having the bird look for that hen, as often a tom will hang up on a decoy (and wait for her to come to him). If he cannot see her, he will often continue forward motion.
I have seen birds run in to a jake decoy, and I have seen mature birds run for the hills when they see them.
One thing I will say, is that it is a different interaction when using decoys... Generally for me, if I am hunting more open areas, I am more likely to use a decoy; if I am hunting in thicker vegetation, I am less likely to use them, and if I am running & gunning I almost never use them.