It really doesn't. Sure, in a hypothetical scenario when we get his transfer fee upfront and we pay the money of other transfers in installments for 5 years, that would mean that we can use his money to buy players worth 5 times as much money as we got from him. But realistically, we will both get his money in installments and pay for the other players in installments. But even if we somehow get his money upfront, we would need to find 50m for those players each of the next 4 years.
This idea that seems to dominate Caf nowadays that selling academy players allows us to spend x5 times as much money works only for accounting purposes. That money still needs to come somehow and that is money we do not have. Sure, we can increase our debt, and buy players but that will make things only worse in the future. Or we could sell stock (Ratcliffe inject his own money and dilute Glazers) and then spend that money on transfers while being ok in books cause of selling Garnacho. But just selling Garnacho won't suddenly allow us to spend 250-300m pounds without getting that money somehow.