I think that was a script someone made because I requested it - I had gotten a project file from someone and the motion blur setting were screwed up and they had migrated to my comps/projects so that script will set all your comps to one setting.
From: "rendernyc" <rendernyc@gmail.com>
To: "After Effects Mail List" <AE-List@media-motion.tv>
Sent: Tuesday, April 29, 2014 2:59:42 PM
Subject: Re: [AE] Master motion blur shutter setting
wow... that sounds like it would make things awfully slow.
i believe only if a precomp is collapsed will it use the master settings.
i dont have it in front of me but RD comp setter might allow you to set those for multiple comps all at once