Do you re-apply FoW?

Curious on people's preferences on this. Do you re-apply the FoW once a party has left an area, or do you leave it revealed and basically marked "explored"? The way I see it, it's encumbent upon the players to each keep their own map sketches on their end, if they want to remember where to go, where certain rooms are, etc. If they get lost in a big dungeon, and can't remember to go left or right...that's not my problem. :D

For my ease I leave off the FoW when they have explored an area since I also use DL. They still have to remember which way to go but with DL it is still dark overall and reveals as they move along.

If the story requires it

Totally depends on the situation but in general the players only see what their tokens see (DL) in my maps and I use FoW to prevent them from seeing areas which have light sources but they don't have LoS to that area.