They say that, I haven't noticed much. My Strawberry Fantasy were all quad/mainlined without tying, my first grow I tied them down. Didn't notice any major differences. But I hate giving anecdotal evidence only. In my opinion the bro-science comes to play in thinking that our manipulation of branch position is beneficial for the plants.
From what I've gathered the true benefit of quad/mainlining I the even sculpting of the plant so that harvest is better in yield and quality due to getting rid of larfy bud and making the plant focus all of its energy on only 8 branches (unless your JKash and do 32

). Bulks up those specific colas and makes trimming easier was well. I just wrote waay too much