Interesting thread :) I have OCD, so I have to be balanced. I got the angel on outside of lower left leg to balance the demon on the right. Even though they have separate meanings, still have to be balanced.
In relation to planning tattoos, yes, all mine are planned and the placement. At the moment, I'm working on getting legs finished. Planning on half sleeves though I think we (me and my tattooist) both know it will eventually be full sleeve, back will be Giger, left ribs will be another memory tattoo to balance the one on right ribs. I know what I want done on stomach and bit under bra, know what I want on top of boobs (bit that can be seen while wearing bra), some of my dresses/tops are low cut so why not? Also have idea of what want done under bra strap on shoulder down. And then all filled. No plans for neck or hands, as work wouldn't allow, but wouldn't rule it out.
When I first started getting tattooed 15 years ago, I didn't think I'd have as much coverage that I do
do. I've also had more people say that I've changed their views of heavily tattooed people and I've inspired a few to start their tattoo journey :)