Well, LST is used to save space and to allow better light penetration for the most part. What topping does is turn one single top cola into two. Topping multiple times doubles the amount of colas each time.
For instance... I keep my Mom plants very small, and a lot of my clippings come from the top of the plant due to height restrictions in my Mom/clone area. One of my moms must have been topped 8-10 times, so if I were ever to flower her, it would likely be ridiculous the amount of colas trying to grow
If you do top, it's generally accepted best practice to do it between the 4th and 5th true node.
You can also look up "FIM"ming.
-spek