Use-cases of forward secrecy/identifying platforms with forward secrecy

One part of The Best Private RTC page I was curious about was the statement regarding forward secrecy. Now I think I have some level of understanding of what the protocol/technology is. My question comes from what use cases the platforms recommended w/out forward secrecy have compared to the ones with it. The page doesn’t really go into detail regarding that part so I was hoping to get answers here.

I was also wondering if there was a way a person can identify if other platforms have forward secrecy. There are links to the pages of element and session that explains why they don’t have forward secrecy, but for more popular ones like facebook and discord, are we able to tell?

Admittedly I haven’t done too much digging on either question so sorry if these are dumb ones.