true enough, but I think there's a little sumthin' to be said for full tanks. There's certainty in it.
The second best is "to the tabs", if so equipped. You KNOW how much you've got.
But for any other level.... Do you really have that many gallons? Do you trust the gauges or dipstick? How precise is it really? How out of level is it when you dipped? How do you know?
....and then there's the other can of worms of having to offload fuel if you have too much for the load you want to take today.
Full fuel is just easier.
Sure it's easier. But with a lot of higher performance airplanes, it's just not practical (and often not a good idea) to keep the tanks full.
I used to fly a Piper Saratoga TC. If I remember right, it had 100 gallon tanks. That's 600 pounds of fuel, and would give an endurance of about 6 hours. There's no way you could fill the seats with adults and fill the tanks. However, they could have made the tanks hold only, say 60 gallons and then maybe you could fill the seats and tanks - but obviously couldn't go as far. Having the larger tanks gives you the flexibility to carry fuel or payload depending on what you need. When I flew it, we NEVER fueled the plane after the flight, because you never knew how many people you'd be flying next time. Instead, we filled up prior to the flight once we knew the load we were carrying. We're so used to filling the 172 up during training that it seems weird to not fill a plane up - but that's exactly what's routine in any kind of commercial passenger-carrying or cargo-carrying operation.
Similarly, the PA-46 I used to fly holds 120 gallons, or 720 pounds of fuel. Same exact situation as the Saratoga.
I now fly a 2018 Baron G58 occasionally for the owners. That thing hold 194 gallons of gas - almost 1200 pounds. If that much is needed, great. But if it's not, you could easily take hundreds of pounds off the gross weight. That's good for all kinds of reasons - single engine climb performance being high on that list.
There's a common saying that "The three most useless things during an emergency are the runway behind you, the altitude above you, and
the fuel left in the fuel truck". That last one is only true if the emergency needs more time to resolve. In just about every other scenario, less fuel is better - engine out in a twin, fire risk if you land off-airport, climb performance (to avoid terrain, icing, weather, whatever), short field landing, etc.
