An approach ban is an altitude at which if the visibility is below the crew/aircraft minima, the pilots must initiate a missed approach.
Some ATC will request your minima before they clear for the approach and will provide you with the actual RVR at the 1000ft/OM.(non-precision/precision).
As a pilot you can request the info too.
But again some play by the rules and some don't.
Seen/heard scary things over the years...