To be the Devil's Advocate:
Why not? We CAN do it, can't we?
So what if cloning things doesn't advance science or solve any world problems like AIDS or hunger? Since when has that stopped science from being science?
Of course, if you have moral or religious (or moraligious, to combine them) issues with the idea of "playing God" then I can see why this question would have a context.
Because out of context it's like asking why the sky is blue. It's just a question that gets just an answer. No one will want to tackle it because there's no guild lines to framing an answer. I think these are the best kinds of questions.
I mean, what if playing around with cloning and replicating of DNA from one creature to its exact copy does indeed lead to inadvertent advances in medicine or technology? Who are we to stand in the way of discovery?
I mean, if it wasn't for the space program doing strange and dangerous things with science we would never have the awesome blenders that allow us to have our margaritas blended instead of on the rocks.
So you really do have to give props for science for coming up with unexpected and non-essential things just by being science.