Subject: "Junk" DNA

I've read that a large part of DNA is "junk"-- that is,

it doesn't code for proteins and serves no apparent purpose.

Is this so?  Why would nature be so extravagantly wasteful?

Or does the "junk" act as some sort of buffer zone against

harmful mutations?  And-- as if I haven't asked enough 

already!-- how do the cell's DNA readers differentiate between

junk and the good stuff?

Thanks for taking my question(s)!

Re: "Junk" DNA