When does an aircraft-carrying submarine make sense?

What would a cruiser-carrier submarine look like, and would it be useful?

It would resemble an M1 or Surcouf with a hangar, but only an I-400-style strike mission gives the aircraft a convincing purpose.

Adding a hangar to an M1- or Surcouf-like cruiser submarine is an unattractive conversion. The Japanese I-400 mission makes more sense on this reading because its aircraft were intended for a limited strike against targets ashore rather than routine scouting. Heavier bombs or fuel-air explosives could strengthen that mission, although the suggestion remains speculative. The result resembles the role of a later SSGN more closely than a conventional carrier.