Tattoos are fuckin' rad. I think we all can agree on that. If you don't agree, what the hell are you doing on a website dedicated to the radness of tattoos? Doesn't make much sense.
A large part of diagnosing skin cancer is the coloration of potentially dangerous moles. Doctors look at the skin in order to see problems, and if the skin is covered in body art, it can make their jobs a lot harder. Skin cancer is one of the most treatable forms of cancer, but it's because doctors are able to diagnose it early. If they can't diagnose it early, it can be deadly.
If you have a particularly knowledgable tattoo artist who is well-versed in the signs of skin cancer, that artist can also identify potential problems.