There was one player on the team that was a pure pitcher. He could not play outfield, was the best pitcher on the team, could play third base pretty well and could hit okay but not with enough power to warrant playing third much. But he was always secure in the knowledge that pitching the first game was always his.
Pinch hitting is the second way. A pinch hitter generally cannot field very well, but can hit with power or with really excellent contact. A few players were pinch hitters. But they didn't have the ability to hit that really made them get used except as a way to just get them into the game.
The tenth fielder is the third way. The tenth fielder often is either someone who can field but can't hit, or can hit but can't field. The coach will prefer one over the other, and start one. But if they are around even, then the one not starting should see some action. Or, if he is the tenth man with the pure pitcher in, as one player was last year, then that means he starts all games the pure pitcher doesn't start pitching.
Pinch running is the last one. As a pinch runner, he has to be fast and smart. He has to be able to take good leads as well, and listen to the basecoach. Pinch runners are generally used in situations when they are greatly needed, to steal a base, or go first to third, or break up a double play. Just to keep the game going longer.
And all four of these are better ways to be sitting on the bench than not. And being two of these, he was content with not starting.