Well basically these transfers are investments for the future. If we buy him now for lets say 10m, loan him for 1-2 years, he performs well, and his value will go up. If Strasbourg would sign him now for these 10m, no way they could sell him to us for these 10m without having UEFA all over our arses.
So basically the idea behind this is that we could get a player that is worth for example 30m for the 10 we initially paid. And then we can decide whether we wanna use him in the squad or sell him elsewhere to make some profit.
Its nothing new really. Roman did the same with Vitesse and his famous loan army.