I have an SSD (used as the system disk) in my iMac, and after noticing that its lifespan (according to S.M.A.R.T.) has ticked down a bit, I started looking at what's writing to the system disk, using iostat, iotop, and fs_usage.
What I discovered is that, even though I have Resume turned off (by checking "Close windows when quitting an application"), Mountain Lion is still writing huge amounts of data to the *savedState folders in ~/Library/Saved Application State, for each application I have open. The only difference with Resume turned off is that it removes the *savedState folder for each app when I quit that app.
Since I use this iMac for work, I typically have quite a few applications open for long periods of time. According to iostat, this is causing over 1 gigabyte of data per hour to be written to savedState. That's 10-12GB in a typical day, not including data I actually write to the drive as I work! Needless to say, this is hammering my SSD and is probably what is decreasing its lifetime.
I've spent a couple of hours googling this problem, and though I've found lots of ways to turn off Resume both globally and per-application, none of them prevent Mountain Lion from continuing to write all this Resume data to the *savedData folders. Does anyone know how to completely turn off Resume and stop all this unnecessary disk I/O?
YOu can get it stop by going to ~/Library/Saved Application State/TextEdit (by example) and delete that file…
(note that the User Library is hidden - one way to get there is to go to your Finder "Go" menu hold the option key to choose "Library")
You can also delete all Saved Application State files
Or use Terminal to turn off Resume globally...
chflags uchg ~/Library/"Saved Application State"
defaults write -g ApplePersistence -bool no