Decoys are most definitely not a necessity when turkey hunting. As many here have mentioned, they can help you and also hurt you.
I base my decoy use first and foremost on weapon selection. With a shotgun, they hurt my odds as they limit my mobility, affect my positioning too strongly, and cause me to hunt more conservatively than I’d like. With a bow, I consider them a strong tool in drawing birds into tight quarters, while diverting their attention from both the sound and motion of my bow being drawn – even when perfectly concealed in a blind.
After that, it’s a matter of season and style of hunting for me. If I’m blind-hunting, I tend to use them more than when out prospecting. Early season they’re much more effective IMO for a number of reasons. More young 2yr old toms running around, more competition for hens that are not yet willing to breed, and less spooking from decoys of other hunters to name only a few. Later season hunts are a different beast, and though that’s when I do a majority of my bowhunting, it’s also when toms have either seen it all, or have been kicked around by other aggressive toms.
If it were me, I’d consider a hen or two if hunting earlier seasons. If budget isn’t too big a problem, I’d have two hens and a strutting tom with real tailfeathers.
Joel