Some clubs do loss to ex-players recall, other profit.
With the return of Paul Pogba to pay Manchester United from 93.2 million pounds (108 million euros) to Juventus for a player that the English club four years past, when it was still with Sir Alex Ferguson at the helm, as well as a free let leave for Turin. Finally caught the Mancunians in court for a shoddy million pounds for the Frenchman, with which the relationship soured was touched. Added up, it makes a loss of over 92 million pounds (107 million euros).
Pogba is not the first player who returns to the old nest, but some clubs get there, also benefit from. Especially Atletico Madrid did a gold case for the return of clubicoon Fernando Torres, for whom, at the time, 32.3 million pounds (37.5 million euros) caught and nothing now would have to pay to another club.
Other well-known examples are the Germans Mats tiny toddlers (from Bayern Munich to Borussia Dortmund and back) and Mario Götze (Dortmund to Bayern and back). A remarkable overview of research firm Statista:
You will find more statistics at Statista