I popcorn my plants even when they are very small because I don't like dealing with thin branches, and I like my main branch to get as thick as possible as quickly as possible. So, should I leave the leaves that form directly across from them, or should I trim the top and the leaf?
Trimming is something that everyone has an opinion on, and nobody knows who is right. Since leaves are there to absorb light and convert it into energy, I think for a plant to grow the fastest, you'd leave them. It's similar to expecting a balloon to grow when you don't put any air into it. Other than that, your question is really vague and hard to guess what it means.
That's one way to look at it. Another way is to think of the leaves as solar panels; they are only so efficient, so when they overlap past a certain point they start to have a negative relationship instead of positive. I.E. past a certain point, the energy needed to keep the leaves alive negates the amount of energy the leaves absorb, hurting growth/yield. I'm not even sure when I stand on the issue, that's why I'm trying both approaches in my grows.