I am perfectly happy with my node modules and the version of node I am running. Why should I keep my node version and the version of my modules updated?
Updates contain
Which lead to
Additionally, new versions contain new features, which might make life easier for you and other developers, who will use the features in modules you might depend upon. If you do not update your node version regularly, you might one day not be able to update your dependencies, even though they contain security fixes or bugfixes you urgently need, which means that you will be forced to make a big update when you have the least time for one.
Peter Scheler
JS enthusiast
Please look first on my explanation of Semver and this article about Semver in npm.
Why you should patch update
Patch updates are fixing bugs and security holes. They make your app more secure and stable, what you are hopefully want.
Why you should minor update
Minor updates are adding features. They don't change the behaviour of your app but make it future proof. They should not have negative side effects to you existing apps, but you need them to receive future patch updates.
Why you should major update / upgrade
Major updates are mostly big clean ups and redesigns. These updates include most times big performance and / or handling improvements and will mostly break your app. So it is a bad idea to upgrade the dependencies of your existing apps. But you can, if you want to use these improvements in your app (intensive tests and modifications will be necessary).
You should use the latest (stable) major versions if you are starting a new project to benefit from the latest improvements.