Quote Originally Posted by Paperplane View Post
To me it's similar to the English 'Right, we're off' which you might say just before you actually set off ie. when the decision to leave immediately is seen as already having been taken (at least by the speaker).
Yes, and I'm reminded of an American slang phrase "We're outa (out of) here!", which is in the present tense, but has a logical future indication. At the time of utterance the act of having left is predicted, yet hasn't taken place. Possibly поехали and пошли were used with a similar sense, at least originally.