Regarding why people use seedboxes
A seedbox is maintained from a distance, commonly via a web-based interface like ruTorrent or TorrentFlux. The little torrent files can be uploaded via a browser to the net interface, or selected right from the host, and all the actual torrent action happens on the machine, and the files are stored on the server until you are prepared to down load or access them in various other way at your leisure. There are also methods to stream movies and music straight from the seedbox. Compared to a property PC, the transfer are mind blowing.
A 1GB video can often be saved on a seedbox in under 60 seconds if you will find different quick seeds sharing the record. Today a seedbox isn't actually anything specific. It's normally only a VPS (virtual private server), or dedicated machine, with specific options completed and the appropriate bittorrent application installed. One way to set up a seedbox is to get a VPS with a hosting company that allows bittorrent, then arrange it your self. That's usually the cheapest way, but not everybody wants to do that setup and configuration themselves however, or do they generally have the knowledge to do it, so that's where the specialty seedbox vendors come in.
Seedbox providers provide a pre-configured server that has all the back-end work and setup already done. All an individual has to do is sign up, log in via their browser per the guidelines, and start torrenting away!