Since I started having problems with Nodejs and npm re El Capitan, I decided to find out exactly why one would want to install locally vs globally. By default, El Capitan still permits us to install npms locally, but not globally. I came across a video post regarding why one would install npm packages locally instead of globally, and decided to share it here.
Installing npm packages locally (docs.npmjs.com)
How to modify System Integrity Protection in El Capitan: (In case you have software hindered by it) Glenn Fleishman, September 30, 2015, MacWorld
El Capitan’s System Integrity Protection will shift utilities’ functions: Glenn Fleishman, July 15, 2015, MacWorld