I used it a few times. One was a choke town and the nation that wanted to get to me had sent hundreds of infantry to attack. I blocked them with armies and used stacks of artillery to auto bombard them.
I used a similar tactic in few other times where lots of units were blocked trying to get to a town and I had some artillery (10-20) and just let them work on the stacks. I would have to adjust from time to time as stacks of units moved or were killed.
I would use units in the town or in the blockers to kill some, once they were all red in a given stack.
Not that many times, when you consider all the games played.