Bad Sides
1) Neymar's come back would slow down the growth of the young stars. The likes of Ansu Fati and Carles Perez hold a lot of dreams for the future. The attacker comeback would starve these young players of game time and consequently affect their scores.
2) There would be murmurs at Camp Nou. There is some peoples associated with the club are not in support of the Brazilian return given the way he left in 2017.
Good Sides
1) It'd keep Lionel Messi happy. The Argentine has reveals he wants a reunion with Neymar. Neymar's comeback would make Barca to ensure their magic power remains happy at Camp Nou and also keep him for long time.
2) It would make Barca's attack stronger. Messi has been weak after Neymar left for PSG. Bringing Neymar back would help re-strengthen the attack and we could witness some MSN magic for more years to come.