Pepe LeFrits
Hey Pep. You do it for a few reasons.
1) FFP - the buying team is at risk of flouting FFP this season if it disburses the amounts consistent with an outright purchase. The loan with obligation defers purchases to a future season. For Arsenal, we would align costs with the extra £60m or so we get from Champions League. Also helpful while we finish our purge and the costs associated with players like Pépé etc to not bear additional costs. Mbappe to PSG was good example of this when it happened
2) Risk sharing - the buy obligation often only becomes active if the player appears in a certain number or percentage of games. This is a get out for the buying club in case they get a dud. Kulusevski has this.