Suppose you want to toggle contents of ALL controls in a form (and its UserControls) with Alt KeyDown to its names or meanings. Then by releasing Alt (KeyUp) they return to their previous old (or even new updated) value.

A) For an instrumentation example, at the beginning labels would be like: (Alt. not pressed)
┌───────────┐
│0.5m
├───────────┤
│23°C
├───────────┤
│77KPa
├───────────┤
│10Kg
└───────────┘
B) And right after pressing Alt, lables will turn into their meanings
┌───────────┐
│Length
├───────────┤
│Temperature
├───────────┤
│Pressure
├───────────┤
│Weight
└───────────┘
C) By releasing Alt key, Paragraph "A" will be repeated.