My 20' Toyota/Dolphin had fixed tag.
My 40' Prevost conversion has liftable tag.
Tags are build for different reason. Toyota used 16' chassis to build 20' coach on it. 10 ' overhang on 20' motorhome is not acceptable.
Lot of gasoline powered motorhome had tag for this purpose. When commercial chassis having originally 4' rear overhang is extended by 8 feet, the tag has to fill up the hole.
On my Prevost tag was build for weigh carrying. Design for carrying passengers, the 6 wheels would not be rated for the weight. My vintage conversion is much lighter and it happen to me to drive 80 miles with tag up not even noticing the difference.
Some chassis have very S***ty suspension that makes white knuckles driving. Adding tag helps to stabilize such animal.
Why liftable on long coach? With tag up, my conversion takes about 8 traffic lanes for U-turn. With tag down add about 3-4.