It looks cool and feels great. Bro science says that flooding the muscles with blood helps them grow. In reality, muscular hypertrophy is induced to a similar degree by high rep, low intensity training training, which would hypothetically result in a pump, and low rep, high intensity training, which likely would not result in a pump. Blood flow restriction (BFR) training, which essentially creates a massive pump at low intensities, has been shown to create larger strength gains when added to high intensity strength training vs. high intensity strength training alone. With that said, "getting a pump" is not the same as true BFR training and is not a substitute. So, to be clear, getting a pump is not necessary for growing muscle. It might happen, it might not, and the muscle will grow as long as the intensity and volume is sufficient.