I'm still just experimenting myself, so take my two cents with a grain of salt.
As I understand it, it's typical to lollipop your plant several days before flipping her to bloom stage. That gives her a little time to recover before the big job ahead of her.
Where and how much? Start at the bottom of the plant and work your way up. Some say, remove anything that doesn't receive direct light or will not yield anything worth keeping.
Others say, start at the top going down, removing the bigger fan leaves to let light penetrate better. Eventually you may experience removing less foliage this way.
In the end, you can do what ever works for your plant and you.
Benefits that I'm aware of: less foliage = better airflow (less chance for mould) Less foliage also means the plant can direct all its energy to the flowers. Instead of having to share its energy amongst the foliage as well. Less foliage also lets light penetrate deeper into the canopy. Hence more usable content.
Hope this helps you nonetheless.