The Cadet scheme has changed from many of its old ways as Atlantic_Conveyor has mentioned.
The Cadets are not employed anymore to save the airline money. This was true in the past.
The reason the airline still continue the scheme is because of the type of pilot it produces. The cadet pilots are exposed to almost the entire operation of the airline while they are undertaking cadet duties in Coventry and West Atlantics HQ in Gothenburg which means when they become a first officer, they, are more often than not, a much more well-rounded pilot than a direct-entry F/O. The cadet scheme will grow alot over the next 2-3 years with current plans.