I’m not sure I use it extensively in day-to-day operations, however, I did write a bit of Emacs Lisp to connect to the System Crafters Live IRC Channel (see here). I also wrote my own templates for a couple of files (pom.xml, an Org file for when I start new projects, etc), and if I create an appropriately named file in the correct directory, Emacs auto-insert functionality kicks in and inserts those templates. If you look at the Crafted Emacs (specifically the modules/crafted-init-config.el) you’ll find an auto-insert example.
Hope that helps.