The wheel hubs are a critical component of any wheel. They perform the task of providing an anchoring point for the spokes, are an anchor point for the wheels to attach to the bike and allow the wheels to spin. Where front wheel hubs are typically pretty basic, rear hubs are more complex and feature a freehub. The freehub is found to perform two functions: to drive the rear wheel and allow it to coast.
With the added speed and weight. Low quality hub won't hold up. A low-quality hub will have more rolling resistance making your efficiency suffer.