Mostly it takes you from thinking 50 requests per second is pretty good to being annoyed that you are only pushing 10,000 per second. It also tends to fail a whole lot less.
It also drastically lowers the amount of processing overhead per page served, after all, there's no dynamic code to process nor are there any database queries to execute.
I don't know, but I found Webby to be just fine... so I'm not sure why we need three static site generators that all seem to function more or less the same...
I would say the same about this conversation. My point being that I could pretty quickly find two previous Hacker News posts that discuss Jekyll and then quickly come around to the question: why do we need another <Webby/StaticMatic/Nanoc>?
One thing I know distinguishes Jekyll is that it uses Liquid which restrcts the templating in a way that makes it safer for some uses than giving the user access to ERB.
In answer to the more general question, I would ask how many scripting languages, text editors, email clients, etc. do we need? Programmers seem to love building things that work exactly as they want. So for all the talk about not reinventing the wheel, we get lots of overlapping toys. I don't think it's necessarily a bad things. More versions can lead to new ideas.
http://github.com/mojombo/jekyll
is static site generation a big pain point for a lot of people?