Before the era of photography, artists had to rely on quick sketches to keep track of potential images for later works. Among the first masters of the quick sketch - called "croquis" by the cognoscenti - was Leonardo da Vinci. Among those who used photographs to help their artistry were Norman Rockwell, Thomas Eakins, and Paul Gauguin
Despite today's ubiquity of cameras - literally in everyone's pocket - it can still be helpful to learn and practice quick sketching. And sometimes a sketch is good enough that a more careful rendering wouldn't be any better. Sometimes if you just draw and don't think about it much, it comes out better.