Simple. Say you have a program which will only take input from one feed at a time - but you want to see the latest updates from more than one through it (for example, Apple's RSS Feed screensaver). Just set up your own, custom feed through FEEDcombine, point your application to it, and you're set!
You can set up as many combined feeds as you want, either using the predefined links or by entering your own favourites. Once you're ready, click the "Generate" button, then bookmark the page that comes up - whether it's a special Live Bookmarks folder in Firefox or a feed in Safari, ready for use in the Apple screensaver.
Because orange is the colour of choice for RSS feeds across the net, quite frankly. Seemed to make sense to stick with the colour scheme...
The script is still in its early stages, so while it should be fairly stable and should work with most feeds, there may still be some bugs. You should note that feeds are cached on these servers - this is to speed up the time in which your feed is generated, processed and sent to your computer. The addresses you access may also be logged.