I do it sometimes. There are quite a few roads that I travel where cops often pull people over for going even 5 mph over the limit and the limit is bizarrely slow (like 30mph). I think that's excessive, so I flash. (BTW, these aren't near schools and the roads are winding and don't have visibility issues. I'm fairly certain it's just a way for the cops to make extra cash.)
This is me, but at the same time, I swear, I drive the roads with some of the most oblivious people in the world. I honestly flash my lights at night so often (because people are driving without their headlights on--and our city isn't especially well lit) that I almost wish Fusions had a "strobe" feature on their headlights. DH and I often bet with one another on how many light-less cars we'll see on our drive home--right now, our over/under is usually 3 for an average of a 5 mile drive.
And daytime during rain or foul weather? Forget about it. Even though in 49 of the 50 states the law is "when your wipers are on, your headlights should be on" the morons that live here almost never have their headlights on. And naturally, they don't use their blinkers to change lanes, make turns either. This is very much a hot button topic in my home.