Industrial overcapacity is usually treated as inefficiency, waste, or failed planning. This commentary uses Lyu et al.'s study of China's aluminum smelting industry to ask when excess industrial capacity may instead function as flexibility infrastructure in a renewable-heavy electricity system. The source paper shows that retained aluminum-smelting overcapacity can enable seasonal operation, shifting electricity demand away from winter load peaks and toward periods of greater renewable availability. Building from that result, this commentary argues that some industrial slack may have option value when it allows material production to move across time. The argument does not defend overcapacity generally. Instead, it proposes a bounded distinction between deadweight capacity and system-valued flexibility. A retained-overcapacity policy should pass a system-value test: whether it reduces electricity-system cost, lowers peak demand, absorbs renewable output, maintains useful employment, produces storable inventory, and aligns private costs with public benefits. The broader implication is that decarbonization changes the economics of timing. The central question is not whether overcapacity is always inefficient, but whether the system has priced the flexibility it provides. Keywords: industrial overcapacity; aluminum smelting; electricity flexibility; decarbonization; renewable energy; industrial policy; grid planning; demand response; heavy industry; China; system cost; industrial slack