The new 2020 Supra is set to come out soonish and the car is covered in ‘fake’ vents. These vents aren’t functional (from the factory) but the plastic filler can be popped out and replaced with real (functional) vents for people that tune the car and make it faster.
One of the reasons Toyota said they didn’t make all those vents functional to begin with, is because it would over cool the engine. Why would this be a bad thing?
Edit: a word
Combustion engines run better and more efficient if they are running at their operating temperature. This is usually at about 85°C for petrol engines. If you keep dissipating the heat generated from the combustion, the engine (or more precisely the controlling unit) will always try to heat the engine up to operating temp. To accomplish that it will use a richer mix (more fuel/less air) which means you’ll burn more fuel than you would need to.
A second factor is the viscosity of the oil lubricating the moving parts in the engine. It will flow better at higher temperatures. So with a cooler engine you will have more wear on your engine components and it needs repairs earlier.
Toyota hybrids for example use oil which flows quicker at lower temperatures because their combustion engines don’t get that hot because they’re turned off so much
The real reason is likely that it is more expensive to manufacture functional vents but makes it looks interesting and high-performance. There’s no reason for the huge vent down the door, the engine is in the front, and the brake vents are also fake
The engine operates most efficiently when it is already moderately hot. Increasing it’s ability to vent heat makes that sweet spot farther away (which is bad if you are just driving casually but good if you are constantly pushing the limit).