A lot of people talk about polishing their site/app/product. Usually referred to in the sense of working on the little details and improving the overall user experience. I think that's great, and something everyone should spend a lot of time doing, but I want to propose that people spend more time "sanding". Sure, it's not quite as sexy of a term, and both polishing and sanding both have the end result of making a thing smooth, but they take different paths to get there. Polishing will make the surface smooth and shiny, but sometimes that is just putting lipstick on a pig. You now have a high-gloss shine, but did you really make it better, or just make it sparkle?
Sanding on the other hand has a different connotation. When you say you're going to sand something, there is a clear idea about what action you're taking, and what the desired result is. Sanding is a reductive process, you're actively removing material. You're smoothing down the corners and getting rid of the rough edges, and I think that should be the goal. Where is this app standing in the user's way? If you look, you'll always find a corner that can be sanded down.
It's really just semantics, but I think you need to do both. If you only have time for one, I'd say sand. I don't care how nice the surface of the desk is if it wobbles because the legs are uneven.