It is residency dependent. I did quite a bit of moonlighting as a resident. However, you should be concerned if you have an abundance of time to moonlight. I did not match with my top choices and the residency I matched to was quite weak surgically, which was why I had so much time to moonlight. It definitely improved my clinical/billing skills and overall I had a hell of a good time during residency. That being said now my surgical skills are behind many of my peers, and I'm out taking surgical courses trying to catch up so I don't cripple someone on the table.