For me I use one style sheet for the front end and another for the back end (since the back end is always recycled from previous projects). I'm not sure why'd you'd choose to use different style sheets for different groups of pages for the front end unless they look a lot different from each other.
Several stylesheets can be hard to manage and could get confusing especially during development, and it also adds to the load time of each page since different pages would require a different external css file to load. At least for 1 css file the caching will be done only once which would mean faster load time for the succeeding pages since they wouldn't have to load another css file. In my opinion, the advantages of using 1 css file outweighs that of using several.
Hope that helps.