Donating art to charity is argued about regularly by artists of all kinds. I can tell you that, as an artist who has donated over 100 works to charity, you should donate art because you want to benefit the cause. Don’t do it to get a profit or exposure. In most cases, it doesn’t bring a lot of new eyes to my work and I don’t make any profit. It costs me nothing but time, though, and I can help more animals find homes, get medical help and other care, that I never could have done if I only donated cash.
That said, my first artwork donation to Hero the Husky launched my entire pet portrait career. I had one really big win. But I can’t predict where another artist might find an opportunity like that. If you’re going to give your time and talent to a cause, do it out of the goodness of your heart and let your support and love be it’s own reward. If you get more “likes” on your facebook page, a commission or two, or some publicity for your work than consider it a nice bonus. This, of course, is just my opinion. I’m going to keep giving as long as I have time and resources to do so because with a few brush strokes I can fill an empty food bowl and that makes me feel great. Chow down, shelter dogs!