Before every game every chess player sees his opponents games, sees the opening repertoire of the opponent and he prepares according to it. Nowadays that preparation goes until the move twenty or even more in the main critical variations. I personally prepare maximum two hours before the game. I prefer to be rested and fresh during the game when the real battle is happening. However I know players who prepare for more the 5 hours, starting the night before the round. Usually they see every game of their opponent and if they remember everything they get good position after the opening. When facing such opponent there are always problems in preparation. That is why is good to have few openings at disposal. This way you will create more pre-game work for your opponent and you will have higher chances to avoid the opening novelties he might have prepared.
Few years ago I noticed that some players have openings which they play few times per year. Usually when a player prepares for the game he neglects these openings and focuses on the openings that are most played, then when the surprise comes! I used and I’m still using this strategy. The bad thing is that this doesn’t always work, eventually the opponents prepare even against those rare openings and the surprise is gone. That is why is good to have an opening that you haven’t played before. Then the surprise can’t be avoided. Of course this can be used ones and then its level of surprise lowers down. It depends from the player to decide when to use your ace and get the psychological advantage. It can be in the last round when the outcome of the game decides the final standings or in some important match.
I used my aces in two games successfully. The first game was played in Macedonian championship where for first (and only so far) time in my life I played French defense with black. The tournament was closed and I was able to prepare for my opponent couple of weeks before. I saw which variation he plays and learned the theory. More, I have had time to prepare the other lines just in case he decided to play something else, which he hasn’t ever played.
The second game was played last year at the chess Olympiad in Tromso, Norway. In the 10th round we, Macedonia, played against Denmark. Since it was penultimate round it was very important for us to win, so as for Denmark. In that game I played Queens Gambit accepted for the first time in my life. My preparation, if I can say preparation, was superficial. Thirty minutes before the game I discussed with my roommate about what opening to play. He suggested it and briefly showed me few set ups. I didn’t know anything else about that opening. In fact that was the first time I played 1. …d7-d5 in my life. I was bluffing and I confused my opponent. He played variation he never played before and soon we got in the position which was unknown to both of us, but I had the psychological advantage and scored the point.
Sometimes these surprises can backfire, the drawback is that the player doesn’t have tournament experience in the particular opening, but the psychological advantage in the opening can usually transform in time advantage on the clock and that can decide the outcome of the game!