Yeah an interesting point, to which I'm not qualified to answer. It comes back to the teams strategists mulling over many many variables and deciding the best pace VS. least risk compromise.....
I know Martin Brundle often talks about 1kg fuel = 2/10s a lap
Fuel is not just fuel in an IC engine. It is also a coolant. The perfect combustion ratio is called stoichiometric, however, ideally you never run an engine like this because combustion temps rise way above the melting point of aluminium (your pistons)... and you invite pre-ignition, or detonation, an uncontrolled explosion in the loosest sense of the term.. so nearly all IC engine on the planet run a tiny bit rich, the extra fuel is called quench, and cools the internal surfaces before and most importantly, during each cycle because after combustion, there is a small amount of fuel unburned to 'soak up' that extra heat. If you can 'safely' remove some of this fuel, you just saved yourself some weight/time etc etc.