Been there. Done that.
Always amused that Apple calls a 'patch' an 'update' or 'upgrade'. Makes it sound a lot less like they've screwed up or are behind the times and aren't we lucky to get something new.
;-)
ADDENDUM: As I understand it from various sites and articles, this 'update' is absolutely critical and is supposed to be the first auto-install update Apple has ever produced, though they have sat on the technology to do so with other patches for over two years. Disregarding this info for a moment, it should be noted it did not auto-install in my case (running 10.10.1) but rather, I had to go to the App Store > Updates and manually activate the download / install myself.
Perhaps their next auto-install update will be one that allows for auto-install updates?