The Canadian rule is that you must have a Pilot Decision making course before being allowed to go down to half a mile vis (normality is one mile).
After listening to some of the people trying to get themselves and others into the Lombard rally last year (shows my age!), when it was down on the deck and clearly not flyable, I think it's a darn good idea, within the obvious limitations, like policing etc
"The least experienced press on, while the more experienced turn back to join the most experienced who didn't take off in the first place"
Phil