Thank you for the question. I can try to answer that.
The most fundamental way of receiving top secret information is to obtain a clearance and to receive it. Having a clearance, whether it's top secret, secret or otherwise, would give someone access to that information if they have a need to know it. That's the general way that classified information is shared within and outside of the government.
The threat reduction measures available to the service allow us to apply a legal test and a legal framework that allow us, in certain instances, to disclose information to someone who does not have a security clearance in order to reduce a threat. That doesn't require the person to whom we're disclosing the information to have a security clearance, but it does constrain us within that framework with the information that we're able to share, because there is a certain legal test to be able to meet the threshold to be able to reduce a threat.
It is a fairly unique way of sharing information. It's not the only way, but that's the main difference.