Do you write every single test for your codebase? Do you have control over every line of code that gets deployed? The purpose of monitoring is to detect issues, because preventing them entirely is next to impossible.
By your logic if you can write perfect integration tests, can't you write perfect application code that doesn't need to be tested?
I agree. Even the default distro that the BeagleBone comes with (Angstrom linux) has Node preloaded onto it, out of the box. And the power that thing offers for $45 seems almost impossible to beat.