I use my sketchbook every day. I can't emphasize enough how important this is to me as an artist. It is the first step for me in beginning a painting. Working quickly from life allows me to learn more about my subjects and helps me truly see what's in front of me, not what I think is there and not what a 2 dimensional photograph shows me. I work mostly with ink, preventing me from taking valuable time to erase. These are just sketches after all; no need to be perfect.
These may look like chicken scratch but it's enough for me to go further and explore a subject for a painting. The most valuable thing I get from my sketches is posture. It helps me take a subject that has been done many times before and execute it in a fresh, new way; a way that only I observed.
I have many artist friends who work from photographs, and I too use my own photos for reference. Everyone works in their own way and I get that. But for me, nothing replaces working from the real thing whenever possible.