I've got RSS feeds of all the webcomics I frequent (and offer it), basically because it's too much to keep up with the updates manually (there are ~45, some more active some not at all right now). Combined with a neat FF-plugin like LiveClick or Feed Sidebar, so I have alarms on them, they are pretty useful. I'm hardly able to keep up with the updates of only a few without RSS and actually a bit too lazy too.
Personally I found RSS quite helping for a site with several updates in a day (this is mostly news sites; so you have all interesting posts in one place and don't need to search the whole site) or for sites which update either rarely or unregurarly (so there is no need to check every day/week etc. whether it had updated or not). Well, these are just thoughts. Basically everything that I can't track with LJ or DA is added into RSS feed, if there is such option