Although the new Ambient Display mode in Android O seems much less interesting than in the previous version (offers a smaller amount of information to display on the screen), it seems that Google has decided to add something novelties that will surely be appreciated by users.
If a feature was introduced in Android Nougat that prevented Ambient Display from being activated if the proximity sensor was covered (ie if the case was closed or the smartphone was put in the pocket). Now, however, Android O adds an additional control. Using the smartphone's proximity sensor once again, you can exit the Ambient Display mode and turn it off completely and at the same time the display can be placed in a pocket or with the case closed. This will prevent accidental activation of smartphones that can cause unintended activities.
In this way we will avoid accidental operation in your bag or in the pocket of the jeans, when it is still not controllable by the user. A small step towards ease of use, but nothing transcendental. Like all the innovations introduced in the Android O Developer Preview it is possible that this function is changed or even eliminated in later versions, if stability is not guaranteed. In any case, this is a subtle change in the management of Ambient Display for Android O.