DAEMON Tools Lite is a tool that can create CD or DVD disc images, and use them in virtual CD or DVD drives. So if you're always swapping discs on your PC then this could save you a great deal of time.
When you have a disc that you know you'll need to access regularly, then, DAEMON Tools Lite allows you to create an image in just a couple of clicks. This then shows up in its Image Catalogue for speedy reloading later, and you can put the real disc away.
And when you want to use that disc, right-click the image, select Mount - or any other VHD, VMDK or TrueCrypt file - and it'll appear in Explorer. You'll be able to access its files, play audio CDs or video DVDs just as though the image was the actual disc. Only without having to keep a pile of discs around your PC, risking them getting scratched.
If you've obtained disc images separately then you can also use DAEMON Tools Lite to access these, without having to burn them to disc. Which is particularly useful, as the program supports a lengthy list of formats, some of which you might not be able to read in any other way: *.b5t, *.b6t, *.bwt, *.ccd, *.cdi*.cue, *.iso, *.isz, *.mds, *.mdx, *.nrg and *.pdi.