In early season hens are vocal and available. the gobbler hears them all yelping and making their own noises and he will come to breed. Hunting pressure, predators play a factor later on in the season. If the gobbler has been called to some he may want something visual to see before he commits. He's anxious early and weary twords the end. Twords the end of season its best to have something that the gobbler can see, now he knows whats making the calls. He may commit or he might just stand there and strut and gobble. If i am hunting a field I will use a hen and a jake or full strut decoy, it will arouse his interest and even up the chances, sometimes. There is no rule for decoys to each his or her own. I've had more success with them than without them. Thats what I love about longbeards, very unpredictable.