This is an excellent exercise, especially if you are lifting by yourself. The reason being, if you cannot get the weight up then gently lower it back to the floor and down by your side without having to let it collapse on top of you. Of course, it is a different matter completely if you are using a barbell. You must have a spotter for obvious safety reasons. Furthermore, it is generally better to have a spotter anytime you are lifting anything over your head.