Flying the Norwegian oil patch it is required to have power to spare on all helideck take-offs. Maximum torque hovering over the helideck is 15% below the maximum allowed for takeoff.
This is to ensure that you during the takeoff procedure achieve sufficent vertical acceleration to clear the helideck edge in case of engine failure at or after reaching TDP (Takeoff Decision Point).
Examples:
S61N: max. torque for takeoff (5 minutes) is 2 x 103 %
Max. torque allowed while hovering for takeoff is 2 x 88 %.
B214ST: max. torque for takeoff (5 minutes) is 100%. Hovering in takeoff position max. torque 85%.
If torque is higher, weight reduction is required.
Having flown the S61 since -89, and the B214St since -92, this has always made sense. I guess the guys who created this procedure during the pioneering days in Norwgian offshore flying knew their trade.
By the way, these limits hardly ever creates any problems. The ST has acceptable performance for most missions. The S61 would most often be limited by other factors, such as wind, drop-down charts or 50' enroute climb perfomance etc.