What does 'Always On Display' button does in Android on Samsung Galaxy S7? What does 'Always On Display' button does in Android on Samsung Galaxy S7?

Please don't say it makes display be always on, because it doesn't.
Quoted from CNET:

According to Samsung, the average smartphone owner checks his or her device nearly 150 times a day: A quick press of the power button to view the time here, and double tap on the screen to view notifications there, apparently adds up fast.
Samsung's solution for this obsessive checking and waking our smartphones is through a feature it calls Always-On Display.
As the name implies, Samsung's latest Galaxy devices are equipped with the fancy new feature.
After locking your device, the screen will remain dimly lit. The default setting is to display the current time, with the information moving around on the screen every few seconds. Alerts for missed calls and text messages are also placed on the screen.

...and additionally from TechRadar:

Where before you'd have to wake the phone to see the time or check your notifications, now the screen permanently displays a clock, calendar or pattern.