I would think the most useful purpose in estimating fuel usage is simply budgeting mileage between refills.
For example, I know that our coach averages 8.5 over the long haul driving 60 to 65 and has done so since the engine was born 68,000 miles ago. This is a very useful number so I can budget two days of travel between fuel stops, or about 60-70 gallons (1/2 tank). Perhaps 3 days in a pinch. I've seen legs averaging 13 and some averaging 6 but they really don't count as stand-a-lone consumption figures.
With the Silverleaf being dead on for both MPG and fuel burnt you can easily plan stops well in advance.
Cost is what cost is but having information for trip planning is very comforting.