#1 Lack of attacking options
After Ousmane Dembele's injury and Munir's departure to Sevilla, Barcelona found themselves with lack of attacking options up front. Luis Suarez and Lionel Messi have been subject to very heavy workload already and lack of options upfront meant that they would have no time to rest.
If anyone of Messi or Suarez gets injured, Barcelona will have to do with playing fringe players, who might not be able to get the possible results. With the arrival of Boateng, the club does not only get variety upfront but it also gives the manager an opportunity to rest the main attackers at the club, keeping them fresh for the big games.
The signing of Boateng can go both ways for the club as well as the player, but there are many good explanations to understand what Barcelona must have thought before signing the player.