When modifying your car, wheel alignment is absolutely crucial.
Every aspect of your driving experience can be affected by alignment, including straight line stability, under-steer, over-steer, acceleration, braking, and tire wear.
Although slight alignments from stock suspension settings are allowed by stock components, they often cannot properly align the car after suspension modifications.
Most cars are set from the factory to have under-steer for optimum tire wear at stock height; under-steer is often undesired from a performance standpoint but is always dependent on driver style.
Therefore, the adjustability of a vehicle's alignment is critical when tuning for speed.
The clock does not lie, and having the vehicle alignment can make seconds of a difference.