What's with the RAR compression on torrents?

Why is it that some torrents of video files come as mutiple RAR archives? I just don't get why they force us through the extra step. For example, I just got the latest episode of The IT Crowd (the second series is heaps better than the rather disappointing first, BTW). The AVI file was 174 megs. The RARed archives totalled 172 megs. Was two megs, a 1% reduction, really worth adding an extra step?

So is there some hidden advantage I'm missing here?

Update: Richard Eldred explains that some distribution methods use free upload sites and the pieces are so it can be easily uploaded, and there are scripts to do the uploading and distribution. He suggests lazy distributors don't bother to torrent the main file.

Michael Kedzierski suggests it's because of USENET. The episodes are probably sourced from news, then put on torrents.

Both explanations make sense actually. Thanks guys.