ive seen alotta people putting up nets and fences to contain how high their plants grow im guessing? if not than what is the point of those?
Your correct in a way....it is for plant training.....it creates a more even grow across a plant, increasing yield Google low stress training (LST)
When you see the people use the term SCROG (SCReen Of Green), that's what they mean... its a form of LST.