A common situation for NUT builds is to verify whether current version of the codebase (e.g. recent and not-yet-packaged release, or a Git branch) solves some issues of an existing deployment. Such tests are simplified if the new build of NUT plays by the same systems integration rules as the already deployed (e.g. package-delivered) version, specifically about filesystem access permissions and configuration file locations.

--enable-inplace-runtime

Tries to detect and pre-set configure defaults for run-time settings (which you can still override if needed, but no longer must specify explicitly to be on same page as the existing setup), e.g.:

If the installed NUT version supports reporting of CONFIG_FLAGS used during its build, the configure script will try to take those values into account when running in this mode.