This is Chapter 2.7 of the JawHacks ebook. See the full Table of Contents here.
There are two reasons adults should Mew despite the fact that Mewing alone will not grow their jaws.
1) Maximize Functional Potential of Your Existing Jaw Structure
Any adult reading this book should begin Mewing (i.e. practicing proper oral habits) immediately in order to maximize the functional potential of the jaw structure they already have, regardless of how deficient those jaws may be.
In the previous chapters, I spoke about Mewing in black and white terms. I suggested that either your jaws are big enough to practice good oral posture and function, or they aren’t.
That was useful for making the theoretical point that Mewing alone shouldn’t be relied upon to grow adult jaw bones. But the present discussion requires more nuance.
Jaws are not either big or small, perfect or terrible. These descriptors are just two extremes of a jaw size continuum that we all exist on.

The bigger your jaws are, the better you can Mew, and vice versa.
But if your jaws are smaller, you can still achieve functional benefits in proportion to whatever structure you’re working with.