Drum determines the pace/flow rate of an operation process and it is the flow rate of the bottleneck operation. Buffer provides enough inventory to make sure the bottleneck operation always has the work to do. Rope sets the restrictive pace for non-bottleneck operations before a bottleneck operation so that just necessary buffer left before a bottleneck operation but not too much buffer produced. The bottleneck capacity determine the overall capacity of an operation system. By simply balancing the capacity of the whole system operation, it will leave too many idle WIP inventories and cause higher carrying cost to store them. What we should do is balancing flow but not capacity to the demand in the market