I guess it's not policy or such, but usually when I send a psi to a LD character (and it seems somewhat important), I think Staff gets notified that it's to a LD player, they'll sometimes send me a message and say 'That person is LD' and then log them off, or just log them off without sending a message. Maybe that doesn't happen as much anymore or it's not official, but enough that I've noticed it as a trend in the past at least.
I also don't think people go LD on purpose for the most part. In my case it's when I'm logging in while it's business hours, and my client disconnects me after not being active for like 2 minutes. Just as well my internet goes out sometimes for an hour or two on end. I think people for the most part try to log off when they can, if not, I'm not aware of the reasons why they would willingly be LD.