Like the old pilot and air screws on carbs, these adjustments are spring loaded so spring pressure is constantly there to prevent the adjustments from moving on their own. Of course the factory seals one of the screws all the way turned in just for the purpose of identifying which body to adjust. Adjust the other one to sync with the sealed screw. That's the yamaha outlined procedure at least. Lots of guys turn out the screws somewhat from there. I'm happy just leaving well enough alone and just syncing one TB to the sealed one. Adjustments will never move on their own either way.
I use mine every 4,000 miles, every time I change oil I check the sync. I mostly do it because I enjoy having the nice tool. It's really not all that critical from my experience at least. In 50,000 miles time I've never had to do more than 1/4 turn of a screw to get sync.