You never want a wire length or cable assembly length to be too short, but a little extra length generally does no harm. This is why we always suggest a “service loop” for wires we connect inside an enclosure. It allows a field technician the flexibility of replacing a terminal or connector without running new wires. Regarding cables, a little extra length seldom causes a problem but if a cable is stretched tight it’s more likely to fail or worse …it might cause intermittent problems. Generally, you should specify lengths with a tolerance of plus 0.500″ (or more for lengths over 24 inches) minus 0.000″. If you can be more generous on the plus side it is always wise to do so. Also, always specify the wire length rather than the assembly length on your drawings if you can.