One feature I really wanted was the "cork board." What this is is basically index cards that you can move around on the screen. For me this is hugely important in plotting. The index cards are hyperlinked to the actual chapters or scenes where you write the text. I was using Visio to do this, and hyperlinking to Word files, but that has its limitations, and Scrivener is specifically designed to do this very well. You can create separate files, and when you need the entire document, you export it as a whole document.
Scrivener has lots of other features, as well.
Download it for free and try it out, though buying it is not exactly a huge investment at $42, http://www.literatureandlatte.com