if you attack malta turn one with the german fleet, it will be more than 2 turns from the atlantic, which is too far. You also have a 60% chance of losing a sub killing the destroyer. so 5(60%*8)+2(66%*3)=7, so, only a 5 ipc gain (average) for attacking malta. It actually ranges from -3 to 12. Anyway, the point is, putting your fleet 2 turns from the atlantic isn’t worth 5 ipc’s. If you send it to gibraltar, you might even get the opportunity of trading the fleet for 2-3 uk planes!
Of course, I’m against it, but if you want to do it to change things up, then be sure to at least use the units on africa to attack it (not ones from italy)