I think trimming plants to get optimum bud structures (usually = max. weight) is very popular, it's just not always called mainlining.
Nuggbucket has a presentation on the subject.
I think the need for techniques like mainlining is often related to the need to maximize weight production indoors.
I have 3 maximally bushy plants outdoors. I think I topped them once. Started flowering about the first of August. I don't think I could make them more bushy.
One of them is an Apollo 11 F3 and she has a lot less branches. If I'd known, I might have done more topping on her.