The soft silicone bristles provide a gentle massage, which pets often enjoy — helps reduce bath-time stress. Good for removing loose hair, dust, dander — especially helpful for pets that shed.
Easier than traditional brushes in the bathtub since you can apply shampoo via the brush (in models with dispenser) and scrub & rinse in one tool. Silicone is often more hygienic than old fabric/sponge brushes: easy to rinse, less prone to bacterial build-up. Makes grooming a bonding activity: scrubbing + massaging your pet can strengthen your bond.