S76 FC PROCS
Yes, I reckon compliance with the Flight Check Procedures Manual is mandatory; it pertains to the aircraft's Certificate of Airworthiness and is not open to interpretation by lesser mortals like us.
By the way, are you doing autos to the ground? That's definitely not in the procedure (tails are expensive) but I can see how you might be concentrated on getting the gear down. Like all the best fun, I reckon it's not approved...
As for the whys and wherefores, we must all defer to Nick.