In most campaigns I've GMed, I usually controlled the henchmen at first to give the player a taste of what their personality was and then passed over control ot the player.
At this point though, as it's not really the player's character, the follower would have some thing hidden from the player and some things might not be fully explained to them. Items say, or history, some regional secret or ability that standard characters don't have.
At that point, unless the player does something to try and benefit at the henchmen's expense, I allow them pretty much full control.