The last time I was aggressive tailgated was on the way home from the hospital with a newborn and a wife just out of abdominal surgery.

Stop it.

What scenario in your mind constitutes deserved tail gating?

Blocking a lane or driving much slower than speed limit without stopping on side to let everyone pass.

And what do you accomplish by said tailgating?

People do get the hint and move over most of the time

Do you think it is worth the risk?

there's little room for "deserving" anything in traffic other than honking

And before attacking with your vehicle itself, you can try counting down from 60. Works every time in my experience.

When is "aggressive tailgate" deserved?

My guess would be not adhering to the "keep right except to pass" signs on the highway. I don't tail gate, but I do find it rather annoying when people block traffic by driving right beside another vehicle rather than passing them and clearing the lane.

So that we can all not adhere to the "maximum" speed signs on the highway to the degree that we prefer :)

I was a passenger while a friend was driving once and he said "I'm already going fast enough. Nobody should be going faster than me anyway." So there's one mentality.