Adding the line "init=/bin/systemd" to the kernel parameters tells the system to boot with "systemd", but it is still a "mixed" installation. If something would go wrong, you could revert to boot with sysvinit and initscripts, erasing the line "init=/bin/systemd" and correct errors.
If everything works, we change to a "pure" systemd installation, installing "systemd-sysvcompat", wich eliminates sysvinit and initscrips. Therefore the line "init=/bin/systemd" can be eliminated, because /sbin/init is a symlink to systemd now.