The long and short squeeze gestures are a really cool idea and this can be used with many application, including the camera app. This pressure sensor that is built into the frame of the phone allows you to control the camera in many ways. For example, a short squeeze motion can turn on the camera app when you are in the home screen or when the phone is locked. This is the easiest way to quickly launch the camera app with very little effort from your side. There is no need to make a slide gesture shake the phone or enter a press any button, it's the most natural way to do it. You are already holding the phone in your hand, so what a more natural way to do it than just use a squeeze motion.
The squeeze motion is not just for launching the camera app. In the camera app, you can use a quick squeeze to take a picture and a long squeeze to turn the rear LED flash on or off.
Here is a video by CNET that demonstrate the squeeze gesture in the camera app. Just look how simple it is to take a picture, no need to press any button, just hold the phone steel and squeeze the HTC U11 phone.
The squeeze gesture can cause the phone to move a bit. Some of you might think that this can cause a blur when shooting in slow shutter speed. The good news is that the rear camera has an optical image stabilization. This mechanism was designed to correct this type of vertical or horizontal movement so there shouldn't be any issues.
The squeeze motion is also very comfortable when taking a selfie shot. There is no need for a timer, no need for special hand waving movement or smile recognition to take the perfect selfie, just squeeze the phone when you want to take the picture and you are done. This removes the inconveniences that we add before this squeeze features was invented by HTC. The HTC U11 really takes advantage of that to make operating the camera more intuitive, fun and convenient. It's a simple thing but I believe it will profoundly ease the phone's operation, not just for the camera, but for many other apps. so chapeau for this HTC.
One last remark. Some people compared the squeeze gesture to like having two buttons on each side of the phone. Although it might seem comparable, with the squeeze gesture you don't need to be to accurate and position your finger at exactly the right place so it's more intuitive and simple. Also the pressure sensor can work with gloves as well, it's not capacitive. So all in all, it's a really nice-to-have feature in my opinion and an advantage that the HTC U11 has that no other phone does, at least for now.