I have seen that people commonly use it to express admiration but it is not a possitive comment due to the fact that you always degrade one of the compared objects... and commonly it goes for the compared guy.
But that's just it. You're basically telling the artist that he/she is not creative and only took ideas from someone else. If you tell a girl she's pretty, you're not comparing her with the supermodel of the day either. So, why do it with art?