For example SYD-PER.... sometimes if you drop several thousand feet below the 100+ headwind, you can save time and make gas. Even though its well below optimum. Many longhaulers are so used to climbing for long range efficiency they refuse to consider the option of dropping so far below optimum. (Unless its for ride)
I remember a year or so ago I was given 2 flight plans for the one sector, one at FL380 and the other I think was at FL280. At FL380 the headwinds were over 150kts, and the flight time was about 6 hours, obviously at FL280 the headwind was a lot less and the flight time a lot less too, possibly up to an hour less, but the fuel burn was about 2 tonnes higher at the lower level even with the shorter flight time.
These are not exact figures but I just remember thinking at the time that if the company wanted the plane to arrive earlier it was going to cost them 2 tonnes of fuel to do it.