With due respect to Mr. Petersen, and as an Emacs user myself, I really can't agree. When I fire up fzf I just type and generally without any thinking I get what I want. Emacs takes some configuration to get to that point; the built in flex completion is, for whatever reason, not as robust in my experience.
In fact, in my current config I've been using fzf (or really skim) for completion within Emacs, via fussy: https://github.com/jojojames/fussy