I've taken to filling up at 3/4 rather than light on. Putting £40 a time in feels better than £150... And I know that if I need to get somewhere I have the fuel to do it.
I would always normally fill (or £99, if thats all they let me have), but it was already carrying an awful lot of weight, so I filled it with enough to get home (plus a good margin, so I didn't have to stop).
I concur that putting small amounts in is a bit pointless for most, but guess if you normally use so little than £40 will last a month, there may be efficiency savings from not lugging 100kg of fuel around. Though if £40 lasts a month, maybe a milk float is a viable option.
That's the kicker. £40 of diesel equates to 100-150 miles, or more than a Leaf or ECorsa can manage... (for reference, my daily commute is a 52 mile round trip)
If you're only doing 150 miles a month, then I would question having need of a car of any fuel... Certainly paying the £20-25k either of the above cost, just to have them sat there makes even less sense.
As an aside, the car park I use has 20 EV/Hybrid spaces, but 0 chargers, rendering the whole debate moot.
As for worrying about the weight of the fuel, that's a waste of time and emotional energy... What you gain in economy from keeping the tank below a quarter is offset by constantly needing to fill up and there is potential for mechanical issues from constantly running low.
Whilst keeping the tank topped up is ostensibly the same, if I can't get fuel for a couple of days, that's much less of an issue than not being able to use the car because the light is on.