It should go without saying, but…
We all get shots where the horizon isn’t level or verticals aren’t vertical. These errors can be fixed in post-processing, but it’s more desirable to get it right in camera as rotating or de-skewing and image can waste a lot of surface area.
This is what happens when you’re too focused on a subject, the horizon is definitely out of level.
Correcting in post means a loss of real estate in the image.