Hey Madman, scrog, training, topping and supercropping are all methods to maximize yields in small grows. You can use one, two or even all of the methods. I top once, then LST and scrog and it works well for my situation. Scrog helps spread out the bud sites in veg so in flower you get max use of the light. Indoor lights are not very good at penetration (compared to the sun). If you have a flat canopy, more buds have access to the light. The other big advantage, IMO is the screen or netting stabilizes heavy colas so you don't need to stake them or tie them from above. Scrog screens are similar to a trellis because it's used to support plants but I think a trellis is usually vertical. Some people do vertical grows with a trellis type scrog screen too.