FOG and sucker holes
Well FOG is a very interesting (and unreliable) situation. Together with its partner in crime 'sucker holes'.
Those who choose to rely on a clearance without 'reliable' alternatives do so at their peril.
If you add on freezing conditions and you are in a machine devoid of protection then Russian roulette seems like a safe game.
We could be socked in for days 'down west' with no alternatives whilst other companies flew overhead on their missions from clear base's.
I always remember a day at lands End when the pleasure flight Cessna taxied out for its 5 min foray, and before reaching the runway it just clamped in an instant when 'the split joined up in a record breaking time', never forgot that, and always ensured 'lots of fuel' as a clear bolt hole may not be as near as you would like when you need it.