Certainly doesn't encourage hens to lay more in my experience and I think you are right Asimov- to some extent it does put them off. One effect I have noticed is a tendency for hens to go broody more often, presumably because they now know their eggs are fertile? Unless you want to breed and you like the noise (we bought out last two because it was just far too quiet here) I wouldn't recommend them. They don't sort out disputes as you would expect them to, they take up coop and run space, eat more food and can regularly injure hens from treading them. We had a really serious injury a couple of years ago and had to separate the poor girl permanently.