Splitting large video files into smaller pieces that can be played independently of each other is a hold over from the days before highspeed internet access when people used to pay for their dial-up access by how much data they transferred. These days people who use premium usenet accounts still have a monthly transfer limit...an example would be 10 bucks a month to download 5 Gigs of data from the premium usenet provider's servers. Usually a still image is also posted with samples of snapshots from the movie with time stamps. This allows people to download the segments of the video clip they are interested in and ignoring the rest if they want and that saves them bandwidth to use for more content relevant to their own interests. Alot of videos and media that are distributed via the internet gets stated on usenet or IRC and using smaller pieces of autonomous data is just easier to move around and work with than larger complete files.