If you are running El Capitan 10.11.x or Sierra 10.12.x you should instal this update NOW. It will solve the latest security issues scalled Meltdown Spectre. Read more here, mixed swedish and english
You who know me are aware that i am superconservative when it comes to new system software. I have NOT installed High Sierra yet but when they launch 10.13.3 i will. By that time all the worst errors should be out. Read more here.
It is close to 6 months since High Sierra was relaesed and that is (according to me) a proper time to wait before you instal new system software on your computer. Also BEFORE you do be sure to check that all non-apple software you use supports the version you are about to instal.
Update 20180124: Is here now but what is really new? On surface its only minor changes. The big change is "under the hood" in form of a new filesystem. This will futureproof yourv computer and will make some operations much faster. Safari, photos and Mail is the "apps" that have been improved so if you use them you will have some impoved experince.. Read more.
Here is a rather clumsy try. They did not bother to hide the emailadress. If you hoover over the link(not clicking) you see the linkadress is way off and the misspelled Apple. If you fall for this...........say no more.