Counter to the common trend, it is not always 'awesome' or 'FTW'. It wreaks havoc with expectations stemming from normal browser defaults, which makes it harder to integrate into existing properties and makes it harder to integrate anything created by third parties that are not operating off of the same opinionated principle.

It's also a total pain in the ass to selectively undo with override rules, as it's reapplied on every element. At the very least you could use box-sizing: inherit I'd think, which makes it at least somewhat easier to selectively cut this awesomely annoying behavior out?