Virtually all engine controls on MB engines of the last fifteen years or so include a knock sensor that will retard timing when spark knock is sensed.
Although I would not recommend it, you could run regular all the time without doing permanent damage to the engine. Because of the automatic adjustments made to timing and other parameters, power and fuel mileage would suffer if you did this.
My recommendation is to run it to about 1/4 tank, fill with premium and forget it. There will be no harm done.
Have a nice weekend,