Jobs queued on one machine while another stood idle

Where several machines can do similar work, allocation tends to follow the operator who usually runs a job type. That is sensible for quality and it concentrates load.

The queue is invisible

Backlog is felt as a general pressure rather than seen per machine. So the shop is late overall while a machine that could take some of the work runs half a shift.

Capability has to be written down

The reason work does not move is often that only one person knows which machines can hold the tolerance. Recorded capability makes reallocation a decision rather than a conversation with whoever is most experienced.

Promising against the constraint

Delivery dates set against overall capacity are optimistic when one machine is the bottleneck. Set against that machine's queue, they are achievable — and the shop can see immediately which orders would relieve or worsen it.