limited slip gives more power to the wheel that is moving the slowest, backwards from an open diff. it kicks in when needed and is more or less forgot about otherwise.
a locker (in this case electronic) is either off, or on. when it is on, both wheels move at the same speed (locked together). when it is on, the diff operates like an open diff. you need to know when you are going to use it/need it and when you dont. in the case of offroading, you could leave it on all the time, but you dont need it all the time.