Paintings often start as line drawings. Eventually, you'll paint over those lines - resulting in a full painting. If you made that line drawing on its own layer in photoshop, you're able to remove those lines in a totally risk-free way! This video shows how to use a layer mask to easily remove the linework and replace it with a painting.
If you don't know about the basics of masks, make sure to watch these three videos first: Masking 101 pt 1, Masking 101 pt 2, and Masking 101 pt 3