After my last grow giving LST a try, I realize that it's easier to control the quantity and size of the buds by topping. I got 5 million buds by doing LST, and they were small and time consuming. If I top, I can control the number exactly. Now that I'm thinking about it, I guess you could too by LST if you cut some bud sites off, but that kinda defeats the purpose of LST.
I think the yield is roughly the same, you just won't get the big colas with LST. The more you have, the smaller they are.
You can start topping whenever you feel the plant can handle it. I usually wait until they have 5 or 6 good nodes, or after 2 or 3 weeks form the cloner, or 3 or 4 weeks from seed. Depending on the variety, you can pretty much count on getting two shoots from the one you cut off. For AK-47 this does not seem to slow the plants' growth one bit. It almost seems like they enjoy it.