I think this will be different for everyone, because everyone's experience, confidence, level of willingness, etc is different.
For me - it also depends on the quilt. If I'm doing something easy like loops, double loops, meander, or something easily replicated all over, I won't mark it. If I'm adding in a motif like a large flower, I will usually mark the flowers or butterflies. If I'm doing Baptist Fans, you betcha I'll mark every darn line!
If I'm doing custom quilting, I'll take a long time to draw out some possible designs on paper, then decide if I need to add any marks. Usually I can just eyeball where the center of a block element is, or do dot to dot type things, but if it's something like 1/3 of the edge of a rectangle, I'll mark where it is since I'm much better at judging where the center of something is vs 1/3.
I'm also inherently lazy, which makes me wonder often why I enjoy quilting! If there are steps I can leave out, I'll totally try it! After I'm done planning, I'm definitely in the jump in and do it boat. I also rarely rip things out so unless it looks horrendous, I'll just keep doing it and it becomes a design choice and the quilts have always washed up fine.
I always check the quilting requirements on my batting to make sure my quilting fulfills the requirements. I don't normally quilt my quilts super closely because while I love how it looks on the quilt, I don't love how it feels when you cuddle up with it. But again, different for everyone.