Difference between npm run watch and npm run watch-poll

watch will listen for file changes, however, on certain systems this won't always work.

watch-poll periodically checks (polls) for changes e.g. every 1000ms it will manually check to see if any files have changed.

https://laravel.com/docs/5.4/mix#running-mix

https://webpack.js.org/configuration/watch/

watch-poll is an alternative to watch in certain enviroments watch might not track changes properly, therefore watch-poll was implemented.

Poll will check the files every x seconds rather than automatically picking up on changes through watching.

You can read up on the docs for a more information about mix.