The first time I was moved, not to tears, but moved to understand how powerful a play can be was "August: Osage County" - That final moment when Violet sprints up those three flights of stairs to the attic and lies in the arms of Johnna, crying "And then they're gone" - very powerful.
As far as moved to tears, it's happened a few times, most recently Whorl Inside a Loop, but as far as having a "Cathartic moment, the first time was the revival of "Journey's End" - My brother was in Afghanistan at the time, so I had a more personal connection to the piece than I otherwise would have had, and in those last three minutes when the lights go down and the theatre is filled with the sounds of war, followed by silence, which is followed by the curtain slowly being lifted again, revealing all the characters who have died in memoriam, with the backdrop of hundreds of names of those who died in battle, I was a mess. I couldn't leave my seat, and just sat there and cried while my partner tried to console me as best he could. I cried for the next twenty minutes.
the second and most recent time was "Airline Highway" - I don't know WHY it touched my so much, but it did. There was a moment when the heartbreaking Julie White looks at Bait boy's girlfriend and just says "You're so pretty"..... at that moment I could see the hopelessness and the Meaningless of these people's existences. I felt so sorry for them, probably because I grew up in the backwoods of Pennsylvania, and felt like I knew a lot of these characters, or at least they reminded me of some of my friends from home. I cried on the N train all the way home that night. I'll never forget it.
"I'm an American, Damnit!!! And if it's three things I don't believe in, it's quitting and math."