They confer various advantages but are not officially supported.
ruby-install allows you to compile and install different versions of Ruby into arbitrary directories.
There is also a sibling, chruby, which handles switching between Ruby versions.
This is useful if you want to customize the build configuration options.
More information about Ruby and its surrounding ecosystem on Free BSD can be found on the Free BSD Ruby Project website.
This can be accomplished very easy with Ruby Version Manager (RVM).