An unlinked production environment is like an accordion. Some processes move faster than the average and some operate more slowly. As a result, parts move through the system at varying speeds, only to end up in piles of inventory scattered along the value stream.
Even with a takt time in place, there can still be some fluctuation in the actual performance of processes, if they are not somehow linked together. This fluctuation gets even more complicated when scheduling is done at multiple places in a value stream. For this reason, a pacemaker is often established. A pacemaker is the single point where a production process is scheduled. The upstream processes don’t produce without a pull signal originating from the pacemaker.