That makes it a lot easier to block ICs from producing sea units, Sea Zones 5, 56, and 62 in particular. More importantly, it makes Subs more effective at blocking those zones, because they get to use their higher attack value, and also be reinforced by air/naval units.
Another situation would be if Germany put a sub in each sea zone around the UK. If Britain puts a Destroyer in each zone to counter, then Germany sends its airforce, while using the Subs as fodder.