Hello Andy,
The originally VSWR doesn’t affect the need of a CMC, but the absent of a CMC may affect the resulting VSWR.
A little bit back in this thread you see my two CMC (in the right part on top).
And like Richard says, the need of a CMC depends from the situation. Because of some problems in the past (5 W out) I’m using my two CMC preventive every time. I couldn’t leave the CMC at home. I don’t know the exact situation on the next summit. And on the summit I save the time for testing the need of CMC.
73, Ludwig