Pretty much this!
…Holy shit. I already caught all the Legendaries in Y, and I still haven’t used my Master Ball. I just realized it.
Thus has it always been:
>backpack full of unused elixirs
I find it’s best to tell yourself WHEN you’ll use those irreplaceable items when you get them. All of my masterballs have labels on them that say ‘Shiny Pokemon that flee’. Having every legendary be a bit tougher to get is nowhere near as painful as watching a shiny abra teleport away… I presume… Hundreds of hours in every game and I still only ever found one shiny.
I only recently encountered my first shiny.
It was a Trapinch.
I accidentally killed it.
Shinies or legendarys without a Smeagle. That’s what the Masterball is for. Except for Red/Blue. Then Mewtwo gets it to the face.