General Subsites are, as you can see from looking at this subsite, static pages containing a bunch of text. They're not the most glamorous things out there, but they get the job done.
What all might one do with something like this? If you don't care about comments, you could use this type of subsite to create a personal blog. If you have complete trust in your fellow man (on this site that translates to: a random group of strangers), you could give everyone permission to edit everything, and treat the subsite as a primitive-sort of Wiki. Otherwise, if you're like me, you'll probably just use these for displaying news and information about something (like a new website).