My rule is "if it's a security fix to plug some kind of vulnerability then you need it, otherwise you don't". Microsoft's website generally says which patches are security fixes, look at the "more information" link for each update in the windows update interface. I personally generally install the security only rollups rather than the full rollups, as the full rollups can sometimes be a little buggy and may on very rare occasions have some telemetry junk in them, plus the full rollups are COLOSSAL to download. To get the security only versions you visit the more info page for each full rollup you are offered, then find on the page (generally above or below the full rollup's entry in a column on the left side of the page) the link to the security only version of the month's patch. The follow a link towards the bottom of the security only update's page to the microsoft update catalogue, download the .msu file and run that .msu file to install the update. If you prefer not to go through this then install the full rollup, either way also always install any standalone security updates, and avoid any standalone updates which offer only a new feature, only a fix for a non-security bug you've never suffered from or only telemetry stuff.
I used to maintain a thread on this site about which updates were necessary and safe to install, but found it increasingly difficult to keep the thread relevant after the so called "patchocalypse" when M$ started distributing patches as big rollups rather than their earlier model of distributing one little thing per update (hence now you get one or two updates per month, and big ones, back then you had loads of updates per month, all small ones). Plus I mostly compute on a linux system thesedays so don't keep up with the state of windows as closely as I did when maintaining that thread.
Edited by rp88, 12 April 2018 - 03:12 PM.
Back on this site, for a while anyway, been so busy the last year.
My systems:2 laptops, intel i3 processors, windows 8.1 installed on the hard-drive and linux mint 17.3 MATE installed to USB