It’s like anything structural from a cable, to a bridge, to an aircraft, the maximum loading etc permitted is less than actual figure at which point it could fail, to allow an extra safety margin, the aircraft’s MAUW limitations will be similar and set the allow optimum performance for runway lengths, reliability, fatigue , longevity etc, similar will be with engine outputs.
i can give one example of it working the opposite way.
The Beechcraft Baron B-58P was designed with a max all up weight of something like 2800lbs , but in the U.K. the cheaper maintenance programme at the time LAMS had a limit of 2730Ibs.
Therefore Beechcraft introduced the P-58PA ( with an A on the end ) for the U.K. market that had a reduced MAUW of something like 2700lbs, thus being under the requirement for the cheaper service scheme and all that was changed was the MAUW and the badge on the side, plus some paperwork,