Written as a test project to try out Ruby on Rails, it basically amounts to a very simple online clipboard, allowing you to store arbitrary text and then access it using a short url.
This is extremely useful functionality if you want to share textual data between two machines. That is, provided the machines do not have email configured. Or access to webmail. Or Jabber. Or other IM protocols - though granted, if they do not support multi-login, that would require two accounts. So I hope you can see why you need this site.