What are the benefits of using Server Hardware versus just placing server software on top of Desktop Hardware?
I've been running a small time webserver for a couple of websites, a blog and a multi-user dungeon for years and am considering upgrading. I've always simply used whatever old desktop machines I had lying around for the server and since my pages don't see a lot of traffic that was fine. Now, however, I'm learning more about running servers in true development environments. I have been exposed to a few of the differences in dedicated server hardware and desktop hardware. I am debating whether it's worth it for me to go the extra mile, spend the extra money and learn about true server hardware in order to assemble a server. Or if I should just stick with what I know and build myself a low power usage multi-core desktop to use that as a server same as I always do.
So the question is, what are the differences between server and desktop hardware and what do you gain by using server hardware for servers?
And for my specific case, are those gains worth the time and effort if it's a small time server for small time projects?
Edit: Yikes that was the longest run-on sentence I've ever written. I must be more tired than I'd thought.