it is required
Rule 0, is required and any game without it just isn't as flexible.
A situation will always occur that there is no written rule for.
Our campaign has tons, due to the strange stuff, and sometimes simulationist level our games reach.
An example, my players were about 2 miles down in this underground complex...within a mountain at a high elevation. SOmething down near the lowest level, caused about 90% of 1 mile radius worth of the complex to turn into water...yes...all the walls, etc turned to water as well as items that failed a save. SO now, players who were 6 levels up from the center of this...the ceiling, sides, floor turned to water. Due to the empty space though below...all the water fell with them in it. Now...they are in a flooded complex with water pouring out if there is a slope/space for it to go.
How would you deal with the upper levels/dirt possibly collapsing onto the group since the lower level support is all gone? Some of it could be built into the sides of the mountain rock that they won't fall...others are being held by other rocks and loose dirt, but now dirt will start falling. But this won't happen instantly for everything. Within about 10 minutes I imagine, as stuff starts dislodging, it willall come down...
I had to quickly make up rules for it so i winged it all and it worked out great.
Then after i got home the next morning, I wrote up whatever i could remember to use it as a similar rule if something like that happens again.
Yes, if you play the game like a MMO - go here, kill creature, take treasure, go there, kill creatures, take treasure, yes, most Rule 0 may not be needed....
but everyone else...it's part of the fun.
Sanjay