What does the ODO submenu/service menu on my 1998 RAV4 do?
I have not been able to find any info anywhere.  

To access the menu,

1-Scroll to total distance with the ignition on then turn ignition off.
2-Turn the ignition on while pressing the ODO button, hold ODO button for 10 seconds. A number between 1-20 will be displayed. 
3-Numbers 1-10 and 11-20 can be selected by repeatedly pressing the ODO button.
4-End the session by pressing and holding the ODO Button for 5 seconds or until the total distance is displayed. Turn ignition off.

5-The number is now stored and will be displayed if this process is repeated. 

I have not identified any change to my instrument panel, or any change to the way the engine runs. 
 Thanks Scotty. I enjoy your videos.