According to forums, it helps players make the necessary adjustments after a fouled pitch.
For some players, there's kind of a burn smell that they smell. It helps them determine how far the ball was from the sweet spot or the center of the barrel of the bat. That way they can make adjustments.
Baseball players and managers are some of the most superstitious athletes in all of sports. If a player or a team gets on a hot streak, then baseball players are willing to do whatever it takes to make sure that it continues.
Some players had routines that they needed to follow before every single game or every start or else they just would not feel right. Check out baseball's 50 weirdest all-time superstitions shared by Bleacherreport.com.