September 1 allows for all major league rosters to expand from the 25-man active roster to the entire 40-man roster. For the Kansas City Royals, those players must be on the 40-man roster by 11:59 PM on August 31 in order to qualify for the postseason. Obviously, that’s not a concern for the 2019 Royals squad but still should be mentioned.
The Royals are in the midst of their rebuild after being on top of the world in 2015. The team lost over 100 games last season and are pace to do so again this year. They definitely need to utilize the month of September to get a long look at some of their prospects that are close to being major league ready.