It takes a couple of minutes for uplink to be received and loaded once the datalink request is sent.How difficult is it and how much time does it take to get upper level winds forecasts and/or observations? It seems the 737 crew was remiss in doing so before they asked for a shortcut though an area with much stronger headwinds.
But you have to have the waypoint set to which those winds are attached in order for the FMC to make reasonable fuel predictions.
So, if you get a “shortcut“ that is, say, 1000 miles, you have to manually build several waypoints along that track, and then send for the winds.
This can be done in your backup route, and only then, can the analysis and comparison of burn and time be done accurately.
It is better, and frankly faster, to have dispatch do the work.
I’ve seen how accurate our flight planning software and processes are. Flying 14 hours across the Pacific, arriving within a couple minutes and a few hundred pounds.
With a 350,000# burn, arriving at destination within 500 lbs is about 0.15% accuracy. Remarkable, frankly.
Not every airline has that degree of accuracy in their flight planning software. Some airlines tend to skimp on software, and IT architecture, leading to low faith in the flight plan itself.
Getting a “shortcut“ offer from ATC may be well-intentioned, but in some cases, it may lead to an increased burn and a slight delay.
A lot of pilots ask for the shortcut out of ignorance. I am quite certain that @Just a civilian pilot is thoughtful and strategic in how he asks but I have sat enough jump seats to know, that there are many pilots who operate at a level far below him.