Sometimes I cut letters to make other letters (a V turned upside down becomes an A if you add a tiny snip of a leftover letter into the middle, that sort of thing) or I use letters of different colors together for a rainbow approach
I hang on to them too. I have used odd letters to make one I need. I sometimes use a single letter as an embellishment. For example, I did a page recently of my granddaughter Katie and use the letter K as a monogram/embellishment.