I remember them being useful when my phone was resting on my desk at work. This was before always on notifications were as prolific and advanced as they are today.

I could wave my hand to check the time. Or see what was causing the most recent notification chime. It sounds really simple but not having to pick up the phone meant reducing distraction.

The Moto X's gestures couldn't be much more than a hand wave due to the simplicity of the sensor. But even so, they kept me from picking up my phone quite a bit.