Man, now that's a good question! I am so tempted to file once mine leaves. I know DB'ing says that it's a wake-up call, or could be, and that this finally shows them the gravity of the situation. Of course you have to be ready for the D because there's a good chance they'll sign and move on.
I don't know if there are any other theories on how it would help. My thought is that if I file once she leaves me and the kids, it shows her that I do not intend to let my family wait for her to take action. It would be a last resort technique to some degree but I would not be doing it as a bluff nor with any expectation that it would stop her foolishness.
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Me: 39/W: 37 D13-D11-S8 M/T 14/20
EA confirmed: 9/13/07 D-Bomb: 9/19/07 OM Gone since 12/18/07 W wants to fix marriage: 3/16/07