“Working on paper is an energising process. Sometimes with canvases, when they’re not going where you want them to go, it can weigh you down. Making a change to a canvas can feel like an extreme or bold move.
… by first experimenting on the works on paper, you are practising your boldness for when you move to canvas. You take more chances because you feel like it isn’t the end of the world if they go wrong.”David Mankin, “Remembering in Paint” by Kate Reeve-Edwards, page 53
Another thing about a painting on canvas is that you can’t crop off a bit unless you take it off the stretchers. You’re stuck with the proportions and size of the canvas you picked. If it’s a painting card or paper all you need is a pair of scissors or a blade and ruler.
A year or so ago the in-house art critic bought me the safety ruler shown in the photo below so I can crop paintings and not my finger tips.