It's only useful assuming that the engines are actually functional. Meanin if we have 4 engines, 3 can be totally destroyed and the sub can still make way. Otherwise it's a bunch of work for little payoff, in fact, a negative payoff.
Assuming that adding them as damage areas allows them to take damage but its NOT functional: You have engines 1 and 2 which provide propulsion/charging. One is destroyed, another damaged. 3 and 4 are also damaged, but they don;t matter cause they don;t make the sub move or charge anything. The damage control teams none the less work on 3 and 4, slowing the repair of the only one left that matters. A nearby DC damages the last remaining one to 100% and it's gone. See what I mean? If they can be 100% functional, then that's a different story.
In reality many boats also had an aux engine. We should really be able to have 4 diesels destroyed utterly and still be able to RTB (good thing for the HOR boats that had self-destructing diesels, lol).
tater