Low Description
There have been several issues with multithreaded_compaction and it's generally discouraged for use, even on SSD based systems. It seems like it would be a good idea to remove it completely from the cassandra.yaml but leave it as a setting for now. That way people can manually add it, but unsuspecting people who don't know about the sharp edges won't enable it on their SSD based systems.
An alternative to removing it from the cassandra.yaml is to add more warnings to the description.