Computer systems can be configured to save power when not in use which also has the benefit of prolonging the life of the hardware.
To this end systems can be set to turn off video output and place the system into various sleep states.
Sleep states are often determined by either configuration settings, inactivity duration or system type, mainly differentiating between desktop or notebook. In the case of notebooks sleep states can also be adjusted based on battery reserves or if the system is connected to the mains.
Sleep states can be light, with the minimum resources in sleep, or deep where nearly everything is in sleep bar the lowest level system functions.
Systems can be woken up by manual actions or automatically, such as network activity to wake up remote systems.
Manual actions are typically pressing on the start button or pressing a key on the keyboard or moving the mouse.
When hardware devices are used to wake up a sleeping system the hardware will send out a signal on the bus that is used to wake up the system and this is needed to wake up systems that are in deep sleep or standby mode as in these states all programs will be in a suspended state.
Unfortunately not all touch screens send out these signals and therefore cannot be used to wake up a system from deep sleep.
However, in systems that are in light sleep with drivers and applications still loaded then the UPDD software will invoke a system function that will wake up the system. This means that for touchscreens that do not send out the 'wake up signal' they will still wake up a system from light sleep.
Touches received when a monitor or system is sleeping are discarded to avoid unintended consequences of touching a blank screen.
Windows sleep modes are discussed in this article.
MacOS sleep modes are described in this article.
Touch screens that can be used to wake a system from deep sleep will show this checkbox on a Windows system. If this checkbox is not shown then the device does not have the ability to wake up a system from deep sleep. We do not know of the equivalent in MacOS.