I agree with Papersak, it's good and bad for the most part.
I believe it's good to try to copy another person's picture by hand from time to time, it helps you learn proportions and poses better. (but that depends if the artist you're copying did it right themselves) But the bad side is that it doesn't help you're creativity...If you're copying someone else's design it will sometimes back fire and hinder you're own style of drawing.
As for me I wouldn't say I'm great at it. Like a Bowser picture I posted on DA, I missed some details on Bowser that made him awesome, lol.
It's so much easier for me to be original because you can make the character as simple or crazy as you see fit...Beautiful thing really. xD