Every little crease plays a role.
When you think of aerodynamics and the cars that benefit most from them, usually hypercars and hypermilers are those you'd consider most likely to benefit from good aerodynamic design. But it has its benefits on sports cars too, even if they aren't capable of hitting 250 mph or returning a 500-mile range. The BMW M3 and M4 have been specially honed to be as aerodynamically efficient as possible, blending downforce with appropriate lift, and the below video from BMW M explains how the designers and engineers tasked with modeling the car worked to create a car that is slippery through the air yet sticks to the track.
Using computational fluid dynamics, sketches, and clay models, BMW's designers are able to determine where the body needs improvements. This helps them find the optimal path of airflow around and through the car to minimize turbulence and enhance cooling, acceleration, and grip. Good aero also helps with good gas mileage, but if there's too much of either lift or downforce, all the hard work refining the engine goes to waste. Even subtle areas like the "air curtains" on the edges of the front bumper have to be refined down to the last millimeter. The profile is also important, while trailing edges and a trunk spoiler at the rear help with good air separation and downforce.
Those front air curtains also have little "flicks" inside for better downforce, while the front lip is designed to guide air to the oil cooler while also enhancing downforce. The underbody has been moved closer to the rear axle in a mild slope, creating a diffuser effect, while "turning vanes" mounted to the underbody also help to enhance negative pressure and downforce. Clearly, BMW has spent a lot of time perfecting these new sports cars, addressing every possible detail from the seats to the chassis tuning. Although some fans of the brand still can't forgive it for putting that face on the car, every other part is certainly better than we could have imagined.