On my Airport Express I can set up SSH advertising for computers on my network.
I have the same option with avahi on a linux server.
What is the utility of doing this ?
When ssh is advertised via bonjour, you can ssh to the linux machine via "ssh hostname". No client side configuration is required is the server changes IP Address, or is using a non-standard port.
Bounjour advertised ssh servers show up automatically in OSX Terminal's File->New Remote Connection menu. In iTerm, the menu is Bookmarks -> Bonjour, or via Right click -> New -> Bonjour.
To enable this on linux (as the OP already has), install avahi, then your /etc/avahi/ssh.service should look like the following. It should be enabled as a boot service.
<service-group> <name replace-wildcards="yes">%h</name> <service> <type>_ssh._tcp</type> <port>22</port> </service> </service-group>