sysusers.d config files allow a package to use declarative
configuration instead of manually written maintainer scripts. This also
allows image-based systems to be created with /usr/ only, and also
allows for factory resetting a system and recreating /etc/ on boot.

https://www.freedesktop.org/software/systemd/man/latest/sysusers.d.html

Note that this does not require a hard dependency on systemd,
debhelper generates depetencies correctly so that they work out
of the box on non-systemd and non-linux Debian builds seamlessly.