I see the benefits of academy players as basically twofold. Bringing 2 or 3 players through each season reduces the need to sign players. It also gives us assets to sell on. We can argue how successful or not we are doing that but it also shows potential recruits that (1) there's a track record of academy graduates making it to the 1st team and (2) that leads to them being in the 'shop window' which can lead to moves to bigger clubs.
All this needs to be set against the cost of running the academy but that's a separate debate!