I just learned this yesterday, literally. So I mean it when I say I am a moron, do not listen to me. I was leveling my scope to my rifle as well, because it made sense, and everything I read before told me to do it. Plus, that is just who I am. I took a frigging eternity using precision machine levels to get everything perfect, only to find out later I was apparently wasting my time.
I have a Sphur on my rifle, and I was using care to ensure I was level when shooting. Inevitably however, I’d look down after a few rounds and find myself canted a hair. I would correct, start over, and what do you know? I’m canted again after a few rounds. Rinse and repeat. Same direction, same amount, every time. By adjusting back to level each time, I was taking myself out of my natural shooting position. More specifically, I was forcing my rifle out of its natural alignment with my body. When I shot, my rifle would shift a little each time towards where it wanted to be, f’ing with my POI (presumably).
The level on the Sphur was actually really helpful in the end. Without it, I may never have known what I was doing. It wasn’t moving much, but it doesn’t take much.
Again, I am no one, and I know nothing. I’d say do exactly what you were planning on doing, and if you stay naturally level, bonus. If not, you at least will have and indicator to show you there is a problem you would not have otherwise have noticed in all likelihood.