What does Private Key User Protected really do?

I am evaluating Comodo EPKI for use by our company to obtain email certificates for use with S/MIME. I’ve read the documentation for this option:

“Private Key User Protected: Place a tick in this check box to place additional protection
on the use of the private key (signing key) associated with the employee’s Certificate.
Additional protection will challenge to the employee to OK the use of the Certificate every
time the private key is used.”

I understand X.509 certificates quite well, but this isn’t clear to me. Does this option have someting to do with encrypting the private key with a passphrase, or is it something else entirely? Thanks.

I’m wondering the same thing. I selected that option and when someone receives my emails with the Digital certificate turned on – even with Encrypted turned off – they get a security warning on their end.