[MetaDark]

It could, depending on your use case, but normally all packages from nixpkgs share the same libcurl, so when libcurl is updated, all packages that depend on it will also be updated.

The old libcurl will still exist on your system to allow you to rollback to previous states of your system, but you can always run nix-collect-garbage if you want to free up disk space.

This is similar to the situation in Arch Linux where pacman keeps all downloaded packages, and you have to run paccache if you want to free space.