I recently prepared hundreds of small panels in order to have a continuous stock at my disposal for daily painting. I was fortunate that a friend was able to cut these to size for me. It was a lot of work to gesso and sand all these panels and they turned out beautifully.
Working small enables the finishing of a work in a short amount of time which is great for experimenting, and it is convenient when traveling. Last year I began painting often on small pieces of mat board that I had a big stack of second hand. When I traveled to Argentina for two months at the end of 2018, I took the mat board pieces to paint on. When I got home to the States, I was inspired to upgrade to MDF (medium density fiberboard). I love the feel of these panels. They're lightweight and inexpensive, but strong. The smallest ones are 2.5 x 2.5 inches, and there are 4 x 4", 6 x 6" and 4 x 5" pieces.