When ‘less fuel’ is talked about, it means trying to do more Reduced Engine Taxi (RET), less APU when it isn’t required and other stuff like that and to at least make people think before they add discretionary fuel.
A legal flight plan using SCF caters for the vast majority of flights. When it looks like it might not, most companies (BA included) expect their commanders to put on whatever they need to make the flight successful. Personally, I don’t think there is such a thing as an unsafe amount of fuel, just an unwise one from a commercial perspective: the point is to get from A to B, not go directly to C, D or F (or back to A) to pick up enough fuel to get to B on the second attempt. As I always say, it’s not how much fuel you set off with, it’s what you do when it’s running out and that can happen irrespective of what you took originally.