(Sorry for the backroom spamming >u<)

Just FYI, sometimes I even merge the sketch to the base layer and totally paint the lines into the actual painting. So the guidelines are literally used in the structure. But in this painting of Henny, I was doing a lot of adjusting and the sketch was very minimal so I didn't build on it. I build the base colour instead. I hope that makes sense! Its all up to your preference and the way that makes you feel more comfortable :) Experiment!