What's the point in using double flats and double sharps when you can just write the note a whole step higher? This has perplexed me for quite a while.
let's say you are in Gb with a Gb key signature. and you wanna borrow a little minor. it might be easier, to drop a "bb" on the B, rather than trying to put Ab and Anatural next to each other in the scale. if you use Bbb then the scale will flow normally on the page without having to keep flipping the A flat-natural back and forth. but don't take my word for it, try it yourself and see which is more convenient