Question: What’s thefunction behind “has associated relay”?
Answer: If you set the  port function to "Direct" then you will get the option in the global advance settings to enable "has associated relay" 
Ifyou activate this function there will be a relay created in the GPO screen for this port.
Youcould use it for example to connect a FOR-22 to a mvx port, but in ECS declare the port as a "direct" with "associated relay"You can now separate the relay function of the FOR-22 away...allowing you to trigger the FOR-22 relay independently rather than the normal mode of FOR-22 which is for the relay to be activated whenever you talk to the FOR-22 port. 
Example you have a number of FOR-22 units in your system but have run out of matrix frame relay GPOs , you can use one of your spare FOR-22 relays instead to fire RED lights, act as a trigger to mixer desk etc..
For more complex installations using the "associated relay" option , the installer can take the RS422 TX data pins directly from the MVX port and use that signal to trigger  3^rd party logic circuit connected to the RS422 TX pins of that port.