When did you last see 1. h4? Months ago? Years ago? When you were among beginners learning chess the same time as you, and they had to check how knights moved after every turn? When was the last time you LOST to h4? Probably never, or at least so long ago that you cannot remember. And that is the point of the opening. I have been using it recently in the blitz room and getting some very good results, including 6/8 wins against top players (I won't name and shame, but I count a top player as above 1900 correspondence. You may not, but keep in mind I myself am well below that, so these are giant killings)
Why play it?
1) To play the desprez opening is to hold up a sign saying "DON'T BOTHER THINKING". Anyone who would play 1. h4 and maybe even 2. h5 can be beaten easily, so black can sit back, relax, and then sit bolt upright when he starts losing, only for it to be too late.
2) Prevent kingside castling from move 1. White shouldn't castle kingside once h4 has been played, and black shouldn't either, because white's only attack is being launched on that side. Both players will keep their kings in the centre, or castle queenside. These both lead to some nice tactical games.
3) It's not actually as bad as it looks, as we'll see later.
1) Comfort with every opening. You need to be familiar with d4, e4, c4, f4, nc3, nf3 and the positions leading from them, because this can transpose into anything. You also need to be aware of, generally speaking, the places where you want pieces to be in the opening. Don't think that playing 1. h4 suddenly makes Na3 ok. That knight still belongs on c3.
2) The ability to judge attacks correctly. Often, games that start with 1. h4 will end with black attacking manically and white attacking manically somewhere else. You need to be able to work out who will succeed first, and be prepared to play defensive moves, but only when they're needed.
3) A fondness for active play.
Some quick lines:
Most common, preventing the rook from coming out.
2. h5 e5
This is the key move. White simply must breakthrough that centre if he is to continue his kingside attack.
If black takes the pawn with the knight, white takes with the bishop. If black takes with the pawn, white plays qxd4 and will win that pawn back. Equal material, and you have your opponent in a game like nothing he has played before. g6 was played in two games against good opposition, and in both I won with qxd4 and Bg5.
If black plays defends the d4 pawn, then white will play c3 or Nf3 at some point, and after swapping off, will play e3 and we are in a normal-looking game, but one that is very open. White is a pawn down, but his rook can be brought into the game very quickly and this can often be forgotten by black.
4. c4 dxc4
And d5 will likely be played. Particularly fun are lines with Bb4, where d5 not only clears the lovely d4 square for the queen, but threatens Qa4+
Also keep in mind when to play Bg5 and spring h6.
5. Nc3 presents few problems for white, but ditto for black.
2. Rh3 d5
3. Re3 Nc6
Maybe someone at some point will fall for 4... Nxd4 5. Qxd4.
5. c4 and there is one last nice line in:
5... nf6 6. cxd5 Qxd5 7. Nc3 Qxd4 8. Qxd4 Nxd4 9. Nxe4 Nc2+ 10. Kd2 Nxa1 11. Nxf6+ Kd8 12. Re8#
Which has only claimed 1 victim so far
Yes, it's unsound. It's very unsound. It will lose your more games than you currently lose in serious chess, but if you're playing someone better than you, it's worth a shot, and if you don't want to play it, I would at least be aware of it.
And if you want to completely disregard it... do you fancy a game?