All of the images I use for my wall drawings are photo-based and drawn on paper first. I draw them multiple times to see what needs to be emphasized and what can be left out.
Of course every drawing is different, but it’s interesting to compare the two versions. The drawings on paper are generally smaller. Paper is much smoother than the surface of the walls, so the walls are more forgiving. It’s almost impossible to erase and correct something on paper, whereas I can usually redo parts of the wall drawings (even though I try to avoid doing this). I can tell, and I imagine other people can as well, when a drawing has been overworked. I love working with (and against) the inconsistencies of the wall surface.
These drawings have been adjusted to the same size. The one on the left is on paper, the one on the right is on the wall: