A person can be experienced at doing X but that does not make X beneficial or factual. I am not trying to be a dick but the difference matters. Specific to mj, it is a resilient plant, you can throw x,y,z at it and it will still produce buds. That does not prove x,y,z is good or bad. Some things are easy to notice visually, but other things, like effects on thc etc etc, not easy at all.
Plants are quite simple in how they work over all (not to trivialise the finer complexities). Botanists figured out that gravity is one of the key reasons a sprout will begin to point up for example. In your specific case, plants close together block each others light to lower canopy and that shuts off growth due to lack of light signals. This could explain why some plants grow slim but tall, to out do compitition. Or, it could be that the signal to shut off lower growth hits another switch to accelerate upper stem growth, essentially putting the plant into reactionary competition mode. I've read of speculation that some tree species actually work together and use this tactic to smother out other competition. Light, intensity, spectrum and duration are known to stimulate stem and leaf growth/amount/leaf size etc. We all witness such triggers with the change to 12/12. The plants as far as I've ever read are very much reactive, not ''free thinking''. It's also easy to see this, if plants had any ability to act freely, they would never grow into a hps bulb and burn.. and continue growing into it even when burning. The plant uses environmental aspects as a simple on/off trigger to grow/stop or veg/flower etc etc.
Yes we can and have learned that certain triggers can be taken advantage of, such as topping (replicates animal grazing) the plant response turns out to be subjectively beneficial to us. But, as many can say, topping serves a human imposed logistical purpose. The people smashing the ball out of the park are doing quick cycle sog. With this perspective you then see that topping has an upside, it's better than poorly trained big plants.. but it also has a big downside, it isn't near as good for annual weight as a proper sog.
This is what I am getting at with the assertions of defoliation late into flower (defoliation is always an ongoing debate). X upside but what downside?.. its more difficult to know. The upside is not inherently obvious either. Not like the topping example.