I hadn't heard of this house-rule until I saw it on Critical Role. Maybe that's why it's so common?
It doesn't seem like it would break the game; it's just one more thing that the characters can do in a round. Sometimes it's hard for me to believe the number of things a character is supposed to be able to do in a six-second window of time. Is this even possible?
But now I'm curious, and also thirsty. Is six seconds enough time for me to punch a punching bag twice, then pull an airline-sized bottle of bourbon out of my pocket, open it, and drink it?
I'll let you know. One sec.
EDIT:
Nope. Using a stopwatch with a lap counter, I observed that it took 6.37 seconds just to get the bottle out of my pocket and twist it open. It took another 7.33 seconds to empty its contents through that tiny bottle opening and into my glass of ice. That's
two Actions, and I haven't even tasted it yet. Being able to do this as a bonus action--say, while I'm sparring with an opponent, or climbing a ladder--is bonkers.
This myth is BUSTED.
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