I Call it "The Workbook"

For a work horse a sketch book is a miniature one but just as powerful. Only using it to sketch nonchalantly will be wasting part of it's usefulness.
I've taken mine all over the place and tried to record scenes from our trips.  On some of the drawings I often include details in writing right on the drawing itself.
When I start an art project I like to do some thumb nail sketches of what the design will be.  I work it out here, first, before putting anything on the canvas.  Then I often go one step further with my major paintings and do a color sketch with paint on a piece of canvas.

But back to the little work horse-you can see what's working and what will definitely not.  It's also very fun to go back and see those sketches.  They have quite a bit of memories involved and it vaults me back in time.

 Art History Moment:  Still talking about "Daybreak" (see image yesterday):  This painting became so popular that during the early 1900's thousands or maybe millions of prints were on the walls of American homes.  At one point the original work disappeared only to turn up on someone's yacht in a climate controlled room-thank goodness.  Can you imagine if they hadn't done that?  The moisture from the sea would have ruined a masterpiece!  It still is in a private collection.