from what I've learned so far (and I'm no pro) the energy that would have been used to grow the entire plant will be used to grow the remains after its topped. If you have damaged leaves/branches you should cut them so the plant does not use the energy repairing itself, instead of growing bigger and stronger, I'm guessing topping works on the same idea.
I only lst'ed the first time. I will do both this time round, because I read everywhere that it is better to top than not to top, if you are doing lst. Topping and lst together is supposed to increase the branching than either method alone. Or something like that.
i see what your saying booradley. maybe some strains i would be better off topping with lst, but now my genetics are well suited for 100% lst. its crowded in there.