Hey all, I had same problem 100+ season pass episodes downloading when I watched them on apple TV (which started to eat up my HD). In the process of trying to stop this I ended up deleting all of my TV shows off my imac and loosing all of my purchased items on apple TV (as i somehow hid the shows)
As per normal the awnser was on various apple boards and partly my fault.
In short:
1) Make sure that you have "download pre-orders when available" disabled in your iTunes preferences by going to iTunes > Preferences under the Store tab. Then, untick
If you have this selected in itunes you are telling itunes to download all new shows that you watch. If you untick it new future shows will not download (you may get a few old shows downloading from old orders but new ones will not download). Note if you manually select "check for available downloads" it can override this option
2) Hiding Episodes - Do not "hide" TV shows, eg by pressing x, this will remove the shows from your computer and apple TV so you will not be able to watch or download them again. To find them again you will need to go into your account online under the cloud and unhide
3) To make it easy for you to redownload episodes in itunes 11, make sure that you have "Show iTunes in the Cloud Purchases" enabled in your iTunes preferences by going to iTunes > Preferences under the Store tab. Then, click OK. You can then redownload the episodes to computer from the main library should you ever need them (otherwise you need to log on to store and then select the purchased items in the Quick Links section per instructions for 10.7 in link below)
Here is a good link on how to re-download tv shows apps etc uising itunes 11 itunes 10 and various other IOS devices
http://support.apple.com/kb/HT2519