Aside from being a fantastic digital canvas, it is a community-based app. To clarify, you create artwork and upload it for "Glops" - similar to "mad props", if you will. People can vote and comment on your creations, giving a sense of purpose to your sketch. Also, the developer is very dedicated, releasing frequent updates, expansions and compo's with prizes.
By the way, I make sketches with big pixels. Check out what some people have done with smaller ones: