Flakes are basically a framework for centrally managing dependencies. Instead of using fetchgit, you’d just make the git repo a flake input and use that input wherever you need to.

The other nice thing they do (that I use) is provide a nice way to define entry points (either ones accessed by a specific nix flake command, or just Nix flake run). Nix flake check and nix flake fmt are the ones I use.

But mostly it’s not anything new, just a (eventually, right now needing to be manually turned on is annoying) nicer UX on top of things that were already possible.