Example
wHO LEFT CAPS LOCK ON?
Who left caps lock on?
Fixing caps lock mistakes
If you typed with caps lock on while pressing Shift at the start of each sentence, you get text like “wHO LEFT CAPS LOCK ON?”. Inverse case turns it back into normal text in one step, with the capitals you meant to type still in place.
How inverse case differs from other converters
Most converters apply a fixed rule, such as “everything lowercase”. Inverse case keeps the information you typed and flips it: every capital becomes lowercase and every lowercase letter becomes a capital. That makes it the right fix for one specific mistake, typing with caps lock on, because the Shift key you pressed for real capitals produced lowercase letters instead.
Other uses
It is also handy for testing how a design copes with unusual capitalization, and for playful text in messages. If you want to undo text that is simply all capitals, sentence case is usually the better choice.