Hey there, long time reader, figured I'd start commenting.
The plant really stretches the first few weeks of bloom, so I like to try to anticipate the stretch. Pre-bloom I only let maybe an inch or 2 grow through the trellis. If they start to poke through more than an inch or 2 then I pull the offending branches further out towards the edges of the trellis to effectively reduce their height and allow the younger shorter branches time time to grow in. If they grow through the trellis too far before switching to bloom then your branches will be really long and skinny by the time of harvest and the trellis will be too far below to offer much support. Then come switch to bloom, during the stretch phase, I will still try to pull fast growing shoots off to the sides to maintain even canopy height, but after a week or so its a pain to try to re-route the fast growers and you can end up snapping branches ect, so I just use skissors and top the greedy ones to maintain even-ness. Imo having equal light intensity among every branch creates uniform bud sizes and maximizes your grow area. After week 3 they'll start to settle down on height growing typically and the topping stops. If the topping resulted in crowding then the weakest looking crowders get pulled. Yes you're cutting buds off, but they'll just cause mold or other issues if they are allowed to grow in too close of proximity.
The SCROG does 2 things for me. It spreads the plant out more horizontally allowing more light to strike the plant, and it provides support during bloom after the branches have grown through and become heavy. Changes the shape, and later helps support the long stems. I have to make sure the height is level in the beginning because any un-level-ness is amplified and compounded as it grows. If it's not level in the beginning, or certain areas are getting more light than others, then the branches with more light grow faster and bigger than the branches with less light and the un-level-ness exacerbates with time. I put a conscious effort to be meticulous early during the windows or times still available for possible manipulation, so that she's happy and optimized later.
I think pre-bloom you want to veg and spread your plant out under the trellis till you can't spread it anymore due to space ect, and then when you switch to bloom is when you allow the spread out tree to grow vertical and through the trellis.
