Going forward, the ports tree will use a "STAGING" directory to build and install the port into, then build a package from the contents of that directory. Only once a package is created, will it be install on the system using the normal pkg tools. The ports tree will not directly install things into the system and manually munge the package database.
IOW, only packages can be installed on a FreeBSD system, and only the pkg tool will do the installation.
Why is this a big deal for people? It makes things a lot simpler in the long run (only one tool to install packages; support for sub-packages; much easier to build custom packages for installation on other systems; etc). And it gets rid of a whole host of problems from having non-pkg_add-related tools mucking around in the package database.
Plus, if one sets an appropriate work directory and makes it user-writable, one can compile ports, install to STAGING, create a package, clean the port, all without being root. Only the final step, installing the package, will require root.