> Distribution would like to override a default. It can patch the file but that is somewhat harder to discover (it would require reading the package source). Alternatively it can add a drop-in. That drop-in goes into /usr too since it's a distribution file.

> User would like to override a default. They should not edit /usr because that belongs to the distribution. They drop their override in /etc.

Larry Wall elegantly solved these problems 38 years ago with the "patch" utility. Debian is a good example of how its use has been standardized to solve these problems.

The patch approach to managing distribution-provided configuration files is superior to the systemd unit approach for at least three reasons:

- Non-experts can read the configuration files from top to bottom in linear order, so the documentation can be inlined by the distribution provider, which means they can add maintainers notes as necessary.

- It also works better than the systemd unit style of configuration for sophisticated users. In particular, if you add a now-incompatible option to the file in the suggested place (next to the documentation and commented out default version of the setting), then the package management system can detect that you've made a potentially breaking change before installing the new software, and ask you what to do. This works in the absence of sophisticated data modeling, schema mapping tools, etc.

- The implementation of all this is factored out and standardized across 1000's of packages, so it only needs to be implemented once and understood once.