Another vote for monitoring my voice while gaming and/or streaming. This isn't just to modulate my volume, it is also to hear the quality and content of what my team mates or audience is hearing so I can tell if any of my settings are screwed up (compression, EQ, etc., my voice must be #1 smexy for the audience of 4). I currently game with open headphones (HD800) and still find monitoring useful, but when I game with closed backs I can't imagine being without it! At first it was awkward, but quickly adjusted to and ultimately valued. Obviously making it optional is ideal, but if the option is either always on or always off, I choose always on.
If you don't wanna hear your own voice... then stop talking lol.
Also, saw the below on the way home. "Hai mah bruh, u haz Mobius plz?"