A mixed Herc crew (Marshalls and RAF) were involved in an inquest to a horse rider's death fairly recently. One of the questions posed was the minimum height that had been flown during the sortie - msd was 250ft. One of the points raised was that if msd was 250ft there is never a legal i.e. authorised reason to be below 250ft. As a result Marshalls were considering raising their planned minimum height to fly e.g. 350ft with radalt at 300 and msd 250.
Legalese but that's the times we live in.