Manifold heat cross over physics and benifits

The relevance is when you start any engine and it is 75 F, 30 F, 0 F or even at running temp. The other relevance is the rate of atomization and the quality of atomization.

Which warms the intake quicker, manifold heat crossover or oil spash? Every time you start and wait 10 - 20 minutes for a hot manifold or wait 5, that is the difference between having to run a richer mixture for longer or for less time.

Cold start rich mixture needed to ensure enough fuel is vaporized and therefore efficiently combustible is dependent to a reasonable extent how warm the floor of the intake is. Intake heats up quite quickly in the area under the carb with crossover heat.
Already discussed is the cooling effect of running fuel and air thru the venturi.

The cooling or an already cool floor of the manifold leads to poor atomization and requires a richer mixture and heavier acc pump squirt to wet the manifold to the point where there is sufficient to surface area of fuel raising the vapor pressure to the point of vaporization. Only then do you have efficient power produced.

This is why you will need richer mixture and more acc pump volume with a cold manifold. The manifold has to be wetter in a cold manifold or you will get lean mixture behaviors. This raw fuel which is necessary for proper F/A ratio during combustion (vaporized fuel mixed with air is the part that makes power) then just runs thru the engine raw, wears the rings and partially vaporizes as it moves from the intake valve to the tail pipe.

Running a cool manifold makes a bit more power. This is why everyone hates exhaust crossovers. That and the cooked oil on the bottom of the intake. The reason cold manifold helps power is only because of the concentration of oxygen per cubic foot of air volume and the cool charge's resistance to expansion prior to explosion helps the charge fit in a smaller place. The best of both worlds is properly vaporized fuel in a dense cool air charge. Hence MPFI.

MPFI eliminates the need for manifold wetting almost entirely as it is not responsible for maintaining a wet environment conducive to fuel vaporization. It doesn't need to maintain even a wet environment in the intake port because the fuel is essentially vapor when it leaves the injector. So, accelerator "Pump" effect or volume is also all but eliminated as well because you don't have to pre-saturate the walls of the intake in order to ensure adequate FA ratio when the throttle blades open.