Vehicle manufacturers install fuel pumps for their stock engines. With most vehicles, you can add minor things like an intake exhaust system and still be within the reserve capacity of the stock fuel pump.
When you install an aftermarket forced induction system you can quickly exceed the capacity of the stock fuel pump. The fuel pump should be upgraded to flow enough fuel volume to maintain the correct fuel pressure in the fuel rail. Sufficient fuel pressure allows the fuel injectors to do their job and properly fuel the engine.