Why not to prune after bloom starts

I was reading up on pruning and thinning plants. There seems to be a consensus not to prune once flowering starts. I'm ok with this advice, but was wondering why not trim off buds that are going to be small, wouldn't more energy go to remaining parts of plant. This my second outdoor grow, skipped last 2 years, so not an expert. In my case I probably should have trimmed prior to flowering. I have already thinned after flowering so too late not to. Plants are probably to 3 weeks into flower. Any thoughts?

I never have problems pruning in flower. You have to be careful though (or so I've been told). Too much pruning can stress a plant which can cause all sorts of problems. This is okay in veg as the plant can be fixed before thrown into flower. But once flowering, any stress effects the final output (quality, quantity, pests, etc).

During the first 2 weeks I do indeed prune small and low buds, as I believe most here do. And any dying leaves or leaves blocking airflow get pruned. I try and stop pruning at week 4 but have done runs where I prune all the way to the end and didn't have negative effects. Just don't prune a punch of leaves at once.

As I've grown as a grower I find myself pruning leaves less and less. As my plants got healthier and I trained them better, there wasn't much need to prune leaves. I still prune the lower and small buds up to week 2 or so.

Pics?

No energy goes to the plants if its leaves are stripped
The leafs blocking out light is broscience