Performance hits and installation of extensions (shared hosting friendly, I guess?)
Also, in small throwaway projects, sometimes setting up Xdebug properly isn’t worth the time and effort. If I’m testing a tutorial demo and checking for bugs, I’ll have a throwaway vagrant box defined which I can scratch after I’m done. The entire ordeal probably wouldn’t take more than 20 minutes, which is far too short to set up Xdebug anyway.