Shawn Colvin was at the end of her rope several years back while touring in promotion of a recent album. Concerts each night, radio interviews and other promotional activities each morning and afternoon, and a bit of sleep between tour stops, she called her manager desperately confiding to him that due to exhaustion, she didn't think she could play that night's show. That was his reply, and she couldn't disagree with him more.
In other news, hip-hop artists love the promotion they get by being on DJ's mixtapes. It's invaluable. Too bad.