Can I delete my iPhoto themes folder (/Library/Application Support/iPhoto/Themes)? I have no interest in ever using them, although I do use iPhoto to store my photos. Will deleting the entire Themes folder mess anything up?
I found if you leave all the folders starting with Printing... and the Assets folder that are in the /Library/Application Support/iPhoto/Themes folder, you can still print.  

Just delete all the other folders and you will regain a chunk of disk space.