To do LST properly, you really do need to top your plant as early as possible (after 5 nodes have formed) so that you have plenty of branches to work with later. You can also let it grow a little tall without topping, and then bend it in a horseshoe so that the highest point of the plant is pulled lower than some other nodes. This is actually topping too, but chemically; you are manipulating the hormones in the plant to favor side shoots that are now exposed to the light.
Topping without LST produces a bush- GREAT if you have multiple points of light and running HPS.
Topping WITH LST allows you to form the plant to suit the type of light you have.