It can be used under any type of lights or in veg or flower.
Basically I use it too keep all my tops about the same height (canopy even), so I get the most of my lighting. I'll also bend fan leaves down under rising branches so the branches get light. This produces more tops and fewer small buds (popcorn buds). Topping plants is a similar concept, trying to produce more tops or making a plant bushier. But with LST you'll still have a main cola.