Mostly because you want your project to just work. You've tested your project with a certain version of Node, and you want to ensure that you use the same exact version when you come back to the project in a year and want to perform some minor updates. You can set the node constraint in package.json, but that doesn't install the correct version of Node for you, unlike nvm.
Well that makes sense, as long as the developer running the code has nvm installed. Does nvm-windows read and install the versions in these nvmrc files? If it does your strategy is indeed pretty cool and I might start doing it myself. I wonder if there's any way to force specific versions of NodeJS without relying on nvm or some compatible tool.
edit: someone here in this thread suggested Volta [0] which seems literally like what I was looking for. No need for the nvmrc as it simply follows what's in the engine property of the package.json. Even better is that it's not a weird massive shell script but instead an actual program written in Rust. I'll have to try it out sometime.
