Didn't know it was good for anything and sold them, but finally noticed they were good for running off abominations, so used it this game for killing RAWR in his cave. Worked good, kept running him off and he finally got stuck in a big boulder, never saw that happen yet with anything, and then I killed him easily; weird.

CaptnJack

I shot it into the sky hoping for something.

I never remember to use the Flare Gun when I have it and I see a Deathclaw.

It's the "primary function" of the Flare Gun. When you first find it in Lonesome Road, there's a note nearby telling that it works against the Tunnelers and Deathclaws, IIRC.