Another great use for those left over scraps from trimming watercolor paper down to size or removing those giant watermarks and embossed logos is practicing strokes.
Let's just say you're trying to get the right stroke for painting those whispy leafless tree limbs. Pick up a scrap of watercolor paper and practice. You don't want those strokes to look all the same. You want variety in shape and size. A patchy scruff of grass, do you have the right color, the right brush, the right amount of paint and water?
A scrap of watercolor paper is perfect for practicing until you get the desired stroke down pat.