The whole os and all settings will be in one config file. So you can replicate your os in a different machine easily.

When you change the config and rebuild the system, a new generation is created. You can easily rollback to previous generations if you mess up. So it pretty much never breaks.

Nixos also has the largest and most updated package repository. It also has features that are very handy for programming like reproducible shell environments etc.

Of course this is just scratching the surface. The learning curve is insane. If you are a functional programmer. Nixos will suit really good.