but i suspect you're talking about tail-recursion rather than TCO specifically. Otherwise the only sensible answer is, why on earth wouldn't you want that if you could have it for free?

so as for tail recursion examples, one nice example i had in the past which made thinking about the problem a lot easier than loops, was when I was designing a 3D maze-like game. The recuraion allowed me to draw each subsequent "step" visible on the screen without having to kniw in advance hiw many steps should be visible. you just draw the "next" room at increasing vanishing distance, until you hit a "wall" (the base case). It was a very simple, elegant result for minimal code; where the equivalent loop would have been long and horrible.

There isn't a killer use case, because tail calls (to yourself or to siblings) can always be easily converted to a loop, and the loop is more idiomatic in most mainstream languages.