It is possible to increase your accuracy if you hold at full draw, but the increase in accuracy is not automatic. It is a skill that has to be learned. It is very likely that someone who is used to releasing the arrow as soon as they reach anchor will have worse accuracy if they start to hold at full draw, for the reasons noted above. It is a choice you have to make. You can certainly be as accurate as you need to be for hunting, and perhaps shoot more fluidly, if you release the arrow as soon as you reach anchor. This assumes you know your effective shooting distance, and stay within that distance. But if you want to increase that effective distance, or compete with the big boys at trad tournaments, then you should probably learn to hold.