为什么在package.json中作为devDependencies咕噜咕噜

I'm new with grunt, I started learning it ten minutes ago and I was wondering why grunt must be listed in the package.json as dependencies. This means that when someone will install my module for node, for example, npm will install to him also grunt. But I actually need grunt just to minify stuff and push them to my git repo and it isn't needed to run actually the node script.I'm new with grunt, I started learning it ten m