The value of a sketchbook.

Here is one of my five minute studies done in Nice while enjoying some vino at the beach restaurant.  A pencil and watercolour wash over some quick pencil drawings of sailing catamarans.  Underneath is a quick watercolour impression of two pigeons waiting for crumbs on the beach.  It's not quite a work of art, but an ideal reminder/memory while reinforcing the anomaly of the sails catching the wind to drive the boats, yet leaving the deck chairs anchored on the beach.  (even though all the beach umbrellas/sunshades had been removed after one or two decided to take flight.)
Simple sketches can say a lot, a bit like taking shorthand notes as an aid to memory.  The combination of the three elements on this page recall the strong wind, (pigeons reluctant to fly around, the lack of umbrellas, and the heeling catamarans) all are now committed to memory and filed away until the time when I wish to emphasise wind in a painting, upon which I will slip this and other sketches out of my collection to help create an image that will convey the required impression. 
This is where these simple sketches, or other simple plein air studies come into their own.  You may get a more detailed rendering of the subjects from a photograph, but you do not get the same memories or hints about the actual reality of the day, how you felt, whether the day was fresh or just humid or cold or even balmy.  These significant details become apparent in an artist's sketch book, not their photo albums.