Perhaps EC155 works for one of those operators who still have the quaint tradition of trying to keep the fare paying customer happy. It is always nice to carry extra fuel but sometimes it is just 'extra' and cancels out any flexibility.
If the crew calculate the IFR fuel required for the flight (which already contains extra for diversions, alternates and MAP etc) they pass weight X to the customer. Customer gives a manifest payload of Y which is 200kg below X. Crew decide to use that extra in fuel so refuel to new amount Z. Customer then decide they have a last minute addition of 2 extra pax. A/C now 200kg over MGW but they had originally told the customer that X was OK.
Some might tell the customer tough titty, others might attempt a defuel and miss the take-off time pissing off everyone. EC155 might just be able to say 'No problem', smile, do the flight safely and everyone is happy.