Recent example.


You arrive into SAN with 7.0 and Approach holds you at the FAF to allow 2 opposite-direction departures out. That will take 8 minutes/700 lbs. Your alternate is ONT and the burn from SAN to ONT is 1.4. According to that instructor, you should divert to ONT now. That would have me land into ONT with 5.6.

Or I could hold, and start the approach with 6.3. Maybe I have to go around. That means I could get to ONT with 4.6. Sorry, but holding for 8 minutes is much easier than dealing with a divert during a simple day trip. Even if another unforeseen event happened that forced a diver to ONT, I still could have landed with 52 minutes of fuel. And if I didn't like how ATC was getting me to ONT, then declare min fuel. There are a lot of backup options if plan A doesn't work.

And before anyone doubts the alternate fuel burns, Delta started using the preferred ATC routings and realistic altitudes to alternates rather than straight-line distances.