Az,.. if you go down,... and manage to do it on the left side, and kill the engine, and the tank isn't ruptured...
...the vac petcock will stop a fuel leak... providing that it's working after the accident...
I'd call it a 35% safety...
...
left side... 50%...
Engine dies... 70%...
tank and petcock in tact... 80%...
___________
all three happen at once... 35%...
... 'course, this only matters if the bike would have caught fire...
I've been down a few times,... even under a truck, and never caught fire...
... chance of fire... maybe 5%...
35% of 5%... = about 2%...
2% chance it will ever help you in a crash...
...