dcgoo
I picked up my Series 9 before 10.1/17.1 software was released. At that time, used double tap to dismiss notifications, one at a time, that popped up on my watch. That took what was always a two-handed operation, to a single hand trick. Glance at my watch, and tap through the notifications, dismissing each, one at a time. Really handy when my opposite arm was tied up!
But that all went away with 10.1, the feature that presumably brings all of the gestures to life. I have been unable to set up that Acknowledge and Dismiss feature since!