Various art teachers, but especially my cartooning teacher, encouraged us to keep sketchbooks and to always be drawing. As I look back through some older books I'm grateful for this advice.
Although I haven't always been drawing as much as I would like to, I'm glad to have the "record" which sketchbooks provide. It gives me a chance to go back and see where and how my skills may have improved. It's also fun to see how I may have been working on a particular idea, refining it, adjusting a pose, etc., until I had a satisfactory finished piece. What's interesting as well, is to be able to see how my confidence may have grown just by looking at the quality and character of my lines and shading.
Chuck Jones ( of Bugs Bunny fame) wrote in his auto-biography about an art teacher who greeted his new students with the following edict: "All of you here have one hundred thousand bad drawings in you. The sooner you get rid of them, the better it will be for everyone." Looking back I can see how I've been working through a good percentage of that hundred thousand myself. But it's encouraging to be able to see them and to sift through them for the occasional gem where things were beginning to finally click.
I'm sure I still have enough of my own personal hundred thousand bad drawings to work through to keep me humble. In the meantime, I'll keep plugging away and expose the occasional better drawing here.