It's about light penetration depth and canopy cover.
My rule is that I lollypop anything 9-12" up from the soil surface. (your distance would be different)- but basically cut all lower bud branches that are not going to make it to the canopy.
After that, I look from the top of the plant down- If I can see the soil- it's fine and only bud covering fan leaves are removed.
If I can not see the soil, then I chop away.
What's important is that the canopy size (bottom to top,height) is sufficient to absorb as much light as possible-
this will vary depending on your light-
18" of canopy is what I usually see with hps.
Disclaimer- I use LED's so the last statement is from others experience, not mine