Ths only thing this applet can do is disable or re-enable your touchpad. If you have no touchpad, it is pointless. If you have only a touchpad and no mouse, then the only thing it can do is give you a way to brick your laptop until you find a mouse you can use to re-enable the touchpad.
The only conceivable non-catastrophic usage of this applet is to manually disable a laptop's touchpad when a mouse is plugged in. This is an extremely niche use case that can already be accomplished by using the "Toggle Touchpad" keyboard shortcut which is exported by the KCM, and would be better served by a setting in the touchpad KCM itself to automatically disable the touchpad when a mouse is plugged in and re-enable it when unplugged, should such a feature be deemed useful. I have my doubts, as Libinput has gotten very good at ignoring false input these days, so I think there is no longer much of a use case for disabling a touchpad at all.
Overall, this applet is not worth the bugs and degradation of the user experience that it can cause. It is too dangerous to exist. Let's delete it.
BUG: 434720 BUG: 434718 BUG: 397210 BUG: 378879 BUG: 430029 BUG: 434717 FIXED-IN: 5.23