There’s another aspect of the game that doubleheaders could impact: pace of play.
In looking at historical data, players and umpires seem to want to get out of the ballpark just a little bit quicker on doubleheader days. Since 1904, the first season for which we have game lengths, nine-inning doubleheader games have been a minute faster (142.2 minutes) than nine-inning single games (143.2 minutes), according to Baseball-Reference.com. Even when there were more doubleheaders in the first half of the 20th century, they were still consistently faster than other games. So while the difference isn’t big, more doubleheaders could perhaps help MLB with its goal to pick up the pace.