Is npm install the same as npm install --save?

npm install without specifying a package name will install the dependencies in your package.json.

npm install gulp-util will install gulp-util without modifying your package.json.

npm install gulp-util --save will install gulp-util and update your package.json, so that in the future when you or someone else runs npm install, they will install gulp-util without needing to specify it. package.json keeps track of your project's dependencies, so that you only have to run npm install after a fresh clone/pull/deployment/reinstall/whatever, instead of needing to manually install all dependencies by specifying their names.

Just running npm install with no arguments, will install everything listed in the dependencies area of the package.json file.

Running npm install <package-name> will install that package only, and will not add the package to the dependencies list in package.json

Running npm install <package-name> --save will install that package only, and will add the package to the dependencies list.

Update for npm 5+:

Running npm install <package-name> will install that package, and will add the package to the dependencies list.