MacOS – Login Script for deleting contents of /private/var/folders

You can safely delete anything in /private/var/folders/ but not the folder itself

sudo rm -rf /private/var/folders/*

Quit all apps before you do & reboot afterwards … and whatever you do, don't touch anything else in /private/var/, and do not delete /private/var/folders/ itself.

Rumor has it that one should not delete /private/var/folders/zz. This article implies otherwise, but if you want to be on the safe side, use

cd /private/var/folders
for i in *; do if [ "$i" != "zz" ]; then sudo rm -rf "$i"; fi; done
sudo rm -rf zz/*

instead.

Looking just at the big parts

• You shouldn't touch anything in /private, as these are files used by OSX.
• Removing unneeded drivers from /Library/Printers shouldn't pose a problem (I only have the Canon drivers for the model I'm actually using in there)
• .../iTunes/iTunes Media/Mobile Applications contains all the apps you've ever purchased. You can, if you want to, delete those which you are not using anymore (and reload them again if necessary), but anything installed in your phone will most probably get resynced on the next sync
• In .../Library/iTunes there might be some old iPhone updates left in iPhone Software Update which can be removed without problems
• .../Library/Developer/Shared contains the Xcode and Development documentation, which can be managed via Xcode directly (or you just remove it and use the web-based version)

I wouldn't bother with the smaller stuff (including iDVD and iPhoto).