Some packages automatically start the daemon they install after installation of that package. For most packages that support automatic clustering that is not what you want.
For example starting a rabbitmq node that should serve as a ram node, will become a disk node anyway if there is no known disk node in the config. To revert it later to a ram node requires a lot of work. Also with cassandra it is best to not start the daemon untill all configuration has finished.
This package will disable automatic start of any installed packages.