In theory, this allows your loved one to look at you, see the signs of a state-change, and look at the list, and tell you, "Dear, you're doing this, that, and the other, and you have these written down as early warning signs of Bad Things." And, with all good luck, this will be enough to help halt the onset of Bad Things, and have whatever sorts of interventions (meds tweak, extra therapy session, a few more sessions in the gym, a good long hot bath and cry, a much-needed few hours off, a chat with someone who doesn't mind venting, whatever works) to halt the progress of Bad Things before they get really bad.
Darkside used to do that for me. He'd see me every weekday morning, and he got to know my warning signs better than I did. And every time I started doing something he thought was a bad sign, he'd call me on it, and demand to know what was wrong. And he'd probe and pry until he found out what it was that was causing me to act oddly, even if it was only something little.
It's the little things that get left untreated that can cause some of the most subtle sneaking problems.
Figment's starting to be able to do that some of the time, but we're trying to resist becoming too close to each other, still. Even though he's let me closer than he's let almost anyone else. I'm starting to be able to call him on things like that, though I don't have the benefit of a written list like the formal technique does.
LJ's been a good tool for that for me, even though reading my past output when in a bad brain-state is painful. I can compare myself to the past, see the improvement, and track when I'm starting to go wonky if I notice a few key things.
A heavy amount of posting, from me, is actually a good sign, especially if I haven't been writing much elsewhere. Writing elsewhere and posting the best stuff to LJ is a good sign. A day without posting is either a really bad sign, a sign of being far too busy to do anything (which will be followed up by a lot of posts), or an indication that I don't have internet access.