I'm someone that reads everything, but also appreciates a useful subject line. One that just contains "." or something similar do my head in. It's still part of the conversation, so use it! And I try and take considerbation of all you threaded users.
I've never seen a subject line with only a period in it. Until now.
I despise subject lines used as part of the message body. Its a subject line!
I voted "threaded" but probably should have said "both."
As an Admin, scanning a thread in a few seconds and being able to see how it's evolving is essential. In my experience, tThreaded is the best mode for accomplishing that. As many here have said, I also pick out the subject lines of posts that I either want to respond to, or that need some kind of Admn action, and respond to those first. If there aren't too many embedded sub-threads, I'll sometimes then switch to flat mode so I can read everything more thoroughly. Sometimes, If a thread is relatively short and has few sub-threads, I view it flat off the bat - pun threads, Middle-earth Conspiracy theories, Scenes from a Hat, etc. all work almost better for me in flat mode.