I love large paintings, but for practical purposes use small sketchbooks. They are portable and small sketches are fast to do.
Yesterday I found this little sparrow dead on the sidewalk, so I brought it home and put it in the freezer, so that I could study it. You can see it in the lower photo. This morning, as a little break from work, I pulled it out and did my first ever full sized sheet. It didn't take long and was really fun to do and unlike a sketchbook, can be hung on the wall. I'll be off to the art supply for more paper tomorrow.