The bevelled margin in an inlay cavity is specifically designed to reduce the amount of exposed cement liner at the restoration interface. This minimizes leakage and protects the luting cement from oral fluids and mechanical wear, thereby enhancing the longevity and seal of the restoration. Unlike retention features, the bevel primarily serves to ensure a better marginal seal and esthetic junction by allowing a thinner, more uniform layer of cement. This approach prevents weakening of the margin and reduces the risk of marginal breakdown over time.

Reference: Sturdevant's Art and Science of Operative Dentistry, Roberson, 6th Edition.