Some time has passed since front derailleurs started disappearing from bicycles. (Though they are still around, of course lol)
The biggest drawback of 1x drivetrains—chain drops—was solved by the spread of chainrings with alternating thick and thin teeth, known as narrow-wide or drop-stop rings.
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Wait a second!!!
Has everyone forgotten that besides the new chainrings, there is another unsung hero that made the 1x drivetrain possible?
Wait, was there something else?
Don't say that—try to remember.
It's the chain stabilizer.
(That's what Shimano calls it. microSHIFT refers to it as a "Ratchet-and-pawl Clutch.")
Since these two are basically always switched ON, it's easy to forget they even exist.
But there is no doubt that this mechanism is another major factor that made 1x drivetrains possible.
The stabilizer that maintains chain tension and prevents drops
The mechanism works by applying resistance to the movement of the arm holding the pulley, preventing the arm from bouncing on rough roads, which in turn prevents the chain from bouncing and dropping.
Basically, once you switch it on, you can just leave it on. There is no need to turn it off.
So why is there an ON-OFF switch?
Only turn it off when removing the wheel
That's right, it's for removing and installing the wheel.
If you leave the switch ON, the arm movement is restricted, making it impossible to remove the wheel. You need to switch it OFF to loosen the movement.
Be sure to switch it back ON after putting the wheel back on.
If you think, "I'll turn it on when I get to the off-road section," you might forget at the crucial moment, so be careful. (If I put it off until later, I definitely forget.)
SRAM has it too
SRAM derailleurs, which don't have a manual stabilizer switch, use a very strong spring pulling the arm toward the rear of the bike, achieving the same effect.
You might think, "Then changing the tire must be a pain," but being the great brand that SRAM is, there is a button with a lock symbol at the pivot point of the arm; if you move the arm by hand and press the button, it locks at an angle that makes it easy to remove the tire.
This system is also very easy to use.
That is the technology hidden in your rear derailleur. It's easy to forget, but it’s working hard for you, so please keep it in the back of your mind.
I'll say it one more time: make sure to switch it ON after putting your wheel back on.