What is the package maintainer ?

Hi,

I am trying to use your template for a project of mine.
Unfortunately, I am not sure I understand the definition of the package maintainer ( myproject_PACKAGING_MAINTAINER_MODE)

I the myproject_PACKAGING_MAINTAINER_MODE considered the build for production and the other is build in development ?

Why is WARNING_AS_ERRORS OFF by default ?
Why is ENAME_SANITIZER_** set within the if<->else ? Could this not just be defined in front of the if ?
Why is myproject_ENABLE_IPO be disabled on Package Maintainer mode ? Would't it make more sende to disable it in NON-PACKAGE_MAINTAINER mode ?

I would be really happy if someone could untangle my confusion a bit :-)