There’s a lot of boring manual work involved when detailing a model, one of which is adding bolts, rivets, panels and various other odds and ends. Just imagine having to duplicate and manually position 2000 bolts on a space ship – and then you realize that you need to change the model a little. Of course you could have been using Linked Duplicates (try Alt+D instead of Shift+D), but you’d still have to manually position each bolt, making sure it fits on the surface properly.
This technique however is really simple, really fast and easily adjustable. No need to place the bolts exactly in the right place and rotate them to fit on the surface properly!