OK, the checkbox seems to have replaced the little speaker (which IMO was cuter). There IS a behavior that I find surprising, but neutral, and that other users may find convenient and/or useful:
it seems that when you disable the driver, whatever the last evaluated value for that particular frame is retained in the parameter as a constant. IOW, the driver stops working but the last evaluated value stays. SO, users must be aware of what frame they are on before clicking that box willy-nilly. AND, do NOT expect to see a visible change in something’s behavior when toggling the checkbox (that was what was throwing me).
If that’s the case I can see how it might be (very?) useful in settling on a particular value before deleting a driver.
I’m still a little blurry on the difference between the little wrench and the checkbox but I’m sure (ha!) it’ll all be clear eventually.