Some chess players excel in only a few particular openings and exclusively use them in their games, regardless of the circumstances. While this strategy allows them to become highly skilled in those specific openings and difficult to catch off guard in the early stages of a game, it also makes it easier for opponents to prepare for the match since they can anticipate which opening lines the player will use.
So, I believe that it pays off to employ a wide portfolio of openings, and occasionally include one or two unusual or less known lines, so the opponent would be pushed outside their comfort zone. For example, let’s take the queen’s pawn opening 1. d4. The most common responses are 1. … d5 and 1. … ♞f6, less frequently 1. … c5 or 1. … f5. However, what if Black suddenly chooses a waiting move 1. … d6?
The opening line 1. d4 d6 2. c4 e5 is called, for some reason, the English Rat Defense. I believe it is more solid than its reputation could suggest, and many good players successfully used it as a surprise weapon.
Black has a decent pawn center, even after the usual queen exchange: 3. dxe5 dxe5 4. ♕xd8+ ♚xd8. After Black plays …c6, the king secures a very safe spot on c7. This move is frequently played by skilled Black players, hence the statistics. White’s pawn advance to c4 is the most notable weakening in the position since it could expose the d4 square, and Black can often establish an outpost on the c5 square for their pieces.
The game can transpose to a similar position from other openings as well. Have a look at the sample game, played by young Tigran Petrosian (who became the ninth World Champion 18 years later). This line is called the Old Indian Defense: Ukrainian Variation: