You don't even know how much space your node_modules folders are taking up until you use this tool!
npkill will scour all subfolders from where you run it and allows you to easily clear out the node_modules folder.
When you need to run the projects in the folders again, you can simple run npm install to restore the dependencies.
Here's what happened for me:
For a longer introduction and description, see Carlos Caballero's article here.