The brake servo reduces the force you need to apply to the pedal when braking. The negative pressure in the engine’s intake manifold is used to achieve this. Both pneumatic and hydraulic systems exist. In cars with power steering, the servo pump may be used for this purpose.
Almost all modern cars, as well as all SEAT models, are equipped with appropriately-sized brake boosters. At a certain brake pressure, the braking force is automatically doubled. You become aware of this due to the fast braking response with short pedal travel, as well as the reduced force required as far down as the ABS control range.