I have one pet peeve on this site - the notorious Link Answer. I review often, and this is an issue that I have seen come up frequently. I know I am being a hypocrite, but here is a list of reasons to not use link-answers.
Ever wonder what happens if they site you linked to goes down? That's right, we have a useless link. Because of this, links are a very bad way to explain answers.
Not Your Own Work
Obviously, links are not your own work. Even if the information is free, it is important to treat the original author and the community with respect. For this reason, it is better to explain the link, and then use a link for credit not explanation.
Lowers the Value of Original Work on Stack Exchange
Having a link answer lowers the value of all answers around it. A new user may ask him or herself Why take the time and effort to ask a question if all I get is a link from a Google Search? This leaves a bad taste in their mouth, and is thus detrimental to the community as a whole.
Please do not use link answers as they are not useful, subject to change, disrespectful, and annoying.