I've never purchased AppleCare + for any iPhones (started with the 3G). I've only purchased it for my Apple Watch, but didn't need it and the two years are up.
My iPhone 6 has lasted 2.5 years with just a slim case and a screen protector (although the screen protector did get cracked/replaced after a drop in a driveway. I will use a case and screen protector on the iPhone X as well. I figure the most likely need for AppleCare + is to replace a broken display, but here are the costs compared to AppleCare + and without:
Cost of replacing screen under AppleCare + = $228 ($199 for AppleCare+ and $29 fee to repair a display under coverage)
Cost of replacing screen without AppleCare+= $279
By skipping Applecare + I save $199 if things go well, and pay an extra $51 if things don't go so well and I crack the display. If things really don't go well, I could be out much more if I end up having to pay $549.
I guess it depends on how risk averse you are, and whether or not the extra cost bothers you. I'm planning on the getting the 256 GB model. Between tax, AppleCare+, and a case+screen protector I'm in for over $1,500! On one hand that makes AppleCare+ an even better bargain IF I ever need to use it for more than a screen replacement. On the other hand that means spending $1,500... on a smartphone. 😵 I guess once you cross the mental barrier of $1,000 though...
I suppose one advantage to getting AppleCare + is that I would be much more willing to go without a screen protector. I've never liked the idea of a screen protector, even though the ones I have used have been fine. Still, there is something about putting a $10 piece of glass over an expensive display that bugs me the same way putting a cheap UV filter over a $1,000 camera lens would.
Before writing this I was firmly in the "not paying for AppleCare +" camp. Now I'm not so sure.