I managed a minor sprain of my left wrist two weeks ago, even though I was wearing my wrist guards. Thing was, I didn't feel the sting until late in the afternoon on the drive home. Two weeks plus and it's slightly tender but in good shape.
I know one of the arguments is that wrist guards reinforce bad habits, and another is that they transmit the impact force further up the arm, doing damage in another location.
From my newbie perspective, I don't want to think how my wrist might feel today had I not been wearing my guard two weeks ago. I'm getting better at falling the "right ways" (and getting even better at not falling at all), but at least in these early stages, it seems the guards have some value.