It is critical to be able to verify the integrity of systems used in military and other applications to ensure that they have not been modified or corrupted. It is of course best to prevent a system from being tampered with. If this can't be done, it is vital to detect tampering. In many cases it is better to prevent a system from operating at all if you can't be sure it hasn't been modified. In all cases it is vital to protect information on the system and especially critical secrets like crypto keys.