Hi,
nice question. Lots of possible answers.
In my household we have 2 iPhone, 2 ATV (1&2) and 5 PCs. Each time I have to sync to iTunes I have skin rash. Because you may ask? We have no proof, but many belive that Apple had made the Windows iTunes version to be; slow, heavy on memory usage and PC resources overall.
iTunes takes too much RAM, takes forever to load.
It is useless for me for :
1- watching movies on HDTV, I use XBMC or Plex on my jailbrocken ATV's.
2- listening to music, I airplay from iPhone to ATV 2.
3- watching movies on PC, I use GomLAB player which is far more user frieny than any other player out there.
4- buying music online, I use http://www.mp3va.com/ it's cheaper.
5- rent videos, I use the ATV.
So to simply put it, I hate iTunes and never use it, unless I want to sync/backup iPhones and of course jailbreak my iDevices.