I was taught the pin never helps a good shot and I still believe it.
Depending on your definition of "good." The flagstick can only hurt a ball that would otherwise go in, but it almost always helps a ball that would miss that still hits the flagstick, and that situation is more common from certain distances than others.
I've seen Johnny Miller even say on a chip that lipped out "see right there, it hit the flagstick!" No, Johnny, it didn't, or the ball wouldn't even fit in the hole (the flagstick was not leaning at all) if it could hit the flagstick when it's barely halfway in the hole.
The flagstick helps shots that would miss but otherwise hit the middle 2.18" of the hole (1.68" + 0.5"). If it's hitting the lip, the flagstick isn't helping. The capture speed on the middle 2.18" is higher, but it's not so high a flagstick hit doesn't hole the ball or keep it closer to the hole than it would have otherwise finished.
Hence my rule: if I'm going to control the distance the ball rolls to within 2-3', I take it out. Outside of that, it stays in because more often than it hurts, it will help. Also, it aids in depth perception.