Given the 2 pc bonus on Tier 21, you are definitely discouraged from ever using pistol shot as Outlaw. I would only ever use it to maintain combo points during mechanics where I have to be off boss.
Strong necro, but after everything that has happened to outlaw since Legion launched, my opinion still hasn't changed. Giving outlaw a free proc ability was one of the worst things blizz has ever done to this spec, I mean it already had issues with resource overflow, and adding that proc just made no sense.