Imaginary time & predictions

The main things that imaginary times gives us are "instantons". These are solutions of the classical equations that exist only in imaginary time. They describe tunneling processes that are classically forbidden, but quantum mechanically allowed.

For simple systems we can derive these tunneling processes by other means such as the WKB approximation, and the instanton predictions agree with both experiment and these alternative derivations. In field theory the alternative methods are harder to do, and for many effects have not been done.

There is at least one imaginary time prediction that we do not want to verify, and this is the decay of a "false vacuum state". Such a decay in our own universe would be fatal to all existing matter, and the life that depends on it.