it's basically a declarative way of writing up machine configuration, including every package that you download/install

as others have mentioned the startup/learning curve is really steep but once you've got a working machine config you've basically documented how to completely setup your machine -- makes it really easy to try new things and roll back!

It is similar to a node-in-a-box distribution, like raspiblitz or umbrel in that you can just "turn on" features and know that they are well-tested and play well with other features. But it's a steeper learning curve to setting up the machine and configuring the features.