Peafowl, like chickens, turkeys, ducks, etc are friendly if you get them young and handle them a lot. Otherwise, they're prone to keep to themselves. They are curious creatures, though, and will sometimes come around just to see what you are up to or what you have in your hand.
As far as uses, they do eat a lot of bugs. But mostly they are just fun to look at.
My experience with them has been that they are gentle birds. But they will eat your grapes and berries...... if they like them. I have one that LOVES raspberries and one that clearly does not like them at all. They eat the ones they can reach or jump to and leave the high ones for me.
I really can't say enough about peacocks. They are beautiful and intelligent birds. Guinea hens are something else again.
As far as shelter, someone told me that, once grown, peafowl are pretty hardy. You can give them shelter or let them roost in the trees. But your young ones need to be protected from weather and predators or you'll definitely suffer losses.
Are you thinking about getting started with peafowl?? If so, let us know how it goes.