ok. i may have a slightly better advantage on understanding.. not only do i care for a child (my 18yo ds) with profound autism, but i'm also autistic/adhd myself AS WELL as having a long term degenerative physical disability.
You ever heard of Spoon theory? If you haven't and you need it explaining please say and i'll expand, but i'm going to use it to explain.
NT/Non Disabled people generally have a lot more spoons to play with during the day than i do. Say.. you'd have 50, and i'm working on 20 to make it through the day.
Say i'm in the PP's position of being on a flight and i use preboarding to 'make my life easier' while i might be fine at that point in the day, still have 15 spoons... and by using preboarding, i'm only using 2 spoons for that activity instead of 8... i don't 'need' preboarding because at that point in the day i have plenty of spoons.
but then my pain from sitting on that flight drains another 5, and the getting off/getting my suitcase/walking through the airport/driving home takes another 8.. I'm down to 2 spoons left to make dinner and get my son to bed, and me to bed.. but that takes 5 spoons.. i've taken 3 from tomorrow, so tomorrow i'll start on 17 spoons instead of 20. Had i not used preboarding, i'd have already been in deficit by the time i drove home by -4 spoons, i can order take out instead of cooking, but sometimes DS won't eat take out, so i have to cook, i still have to put son to bed, and me to bed, so that's 2 spoons, i'm now starting tomorrow on -9 spoons.
I might not 'need' that accommodation at the moment it happens, but that doesn't mean that not using it won't massively impact the rest of my day, and the day after.. so i use the accommodation i don't 'need' and that isn't abusing it.
I don't understand why you're struggling to get that?