It's a very hypermodern system for black that isn't as popular as other opening moves but not for lack of results.
I don't play it myself and wouldn't recommend it to any club-level players, and especially wouldn't recommend it to beginners (just play 1..e5 and shut up - don't be cute). The fact is that without the requisite knowledge it's too easy to end up worse and cramped for space. But in the hands of someone who really knows what they're doing it can be very dynamic and give good winning chances as black, particularly when your opponent had prepared for something else. Theoretically, it's actually quite sound.
Also, you're not really committing the "move the same piece twice" violation when your opponent wastes a tempo themselves by pushing the same pawn twice. And if they try to attack the knight again they're gonna have weaknesses which is good compensation for the lost time.
For example, if white plays 3. c4, then white moves the knight to b6 ... and the d4 square, a very important square in the white position, is ruined and ripe for black occupation. If he pushes again, 4. c5 - well now it's just ridiculous. After moving the knight back to d5 (which is now a very cozy home in the middle of the board), look at what white has done: pretty much the entire d-file has been weakened, and those pawns must be defended (which will weaken white's position even more). In a GM game white would, already, be dead lost. And just like that. So it's not so simple to get an advantage with white. It's a good opening choice for theoretical players who prefer dynamic positions.
It is definitely a more complicated opening than the kings pawn.
Right. This opening is not about winning tempi but about luring the white pawns forwards to attack the space that will be created backwards of this pawns. The opening is valid as other aswers to 1.e4 are too. 1...e5 1...e6 1....c5 1...c6 1....Nf6 1....d6 1....Nc6 it is all playable.
We voted that there would be no vote. Our silence pertaining to the proposed vote was a vote in and of itself (not to vote). Cheerio!