It's all a big con to get around financial fair play. When they sell the player in the first place 100% of the transfer fee goes into that year's accounts as income, when they buy him back the transfer fee is divided by the length of the contract. It's fiddling the books and many PL teams have been doing it recently and it's not going to end well.
All this goes right over my head, but how does spending more money help you out? It is it just a delaying tactic?