Credit on the inheritence idea to Jon Neal here, who says:
This will give you the same result, and make it easier to change the box-sizing in plugins or other components that leverage other behavior.
Explaining further, let's say you have a component that was just designed to work with the default content-boxbox-sizing. You just wanted to use it and not mess with it.
/* designed to work in default box-sizing */
/* in your page, you could reset it to normal */
The trouble is, this doesn't actually reset the entire component. Perhaps there is a <header> inside that component that expects to be in a content-box world. If this selector is in your CSS, in "the old way" of doing a box-sizing reset...
/* This selector is in most "old way" box-sizing resets */
Then that header isn't content-box as you might expect, it's border-box. Like:
This isn't a majorly huge thing. You might already be using the box-sizing reset the "old way" and never have gotten bit by it. That's the case for me. But as long as we're promoting a "best practice" style snippet, we might as well hone it to be the best it can be.