I've had so many! LOL but then I started quilting before the rotary revolution and was self-taught.
But yes, first rotary cutter/mat/ruler changed my life.
The book Scrap Quilts by Judy Martin changed my quilting career, before that all my quilts were "planned" and I had never seen a scrap quilt I liked. Now I quilt almost entirely with scraps -- still planned, but dozens if not hundreds of fabrics instead of 5-6. The directions are a bit dated now but I'm still such a fan of the book!
https://www.amazon.com/Scrap-Quilts-.../dp/096029709X
As I've been dealing with progressive vision loss I've become a fan of what I used to disdain as "fabric wasteful" techniques. Now I'm a big believer in cutting large and trimming down, it only takes a tiny bit more time and makes my end results better. My favorite way to make triangles now is with a square by drawing a diagonal line across the fabric and sewing on the line, then trimming off the excess. Especially in small triangles the amount of fabric waste is negligible and it is fast and precise. And no need to worry about adding 7/8ths to the finished size dimension for the right cut.