Well, one reason for knowing about the list is so you know the fonts that other people are likely to have on their computers. If you list special fonts in the font-family for elements on your site, but they don't have them, they won't see that font. Knowing the for-sure fonts that others have allows you to specify fonts rather than leaving to the default, such as Times New Roman.
Here's a nice reference, and a recent one, on pre-installed fonts for macs, linux and windows machines:
http://www.apaddedcell.com/web-fonts
CWM Post with Helpful Links for Web Design Newbies<