So "cutting off" the allies in their retreat to OZ is a major priority? To starve them out? Or to force them to die in place?
By taking several lvl 4 airfields or cruising carriers around DEI, you achieve several important things:
1. You make it too dangerous for him to attack your landing TFs with surface fleets. I had a jap opponend not doing this and sank him 1BB, 3CA, 3CL +DDs with the Dutch and british ships. If he had Bettys everywhere, it were too dagnerous.
2. You sink the fleeing enemy shipping. This isn't as important as sinking 100 dutch/british/US AKs from DEI, Malaya and PI doesn't change anything. It also doesn't give you too much points - still, it's better than nothing and reminds your opponent better not to get into betty range. The important ships (warships, large APs) usually are too fast and consequently out of range, soon, to catch several of them.
3. You sink enemy fuel and oil transports comeing from DEI. THe allies are desperatly short of fuel in Australia at the beginning. I managed to sink the mini-KB in January 42 in the Java Sea with the two allied CVs initially off PH by shipping every ton of fuel available from DEI to Port Morsby and Darwin. If he had captured the lvl 4 airfields, neither would my CVs have appeared nore would I had have the chance to ship enough fuel for them and their escorts...
4. You sink enemy ships carrying reinforcements and supplies to Singapoore, Manila and Java.
Without any doubt: I am the spawn of evil - and the Bavarian Beer Monster (BBM)!
There's only one bad word and that's taxes. If any other word is good enough for sailors; it's good enough for you. - Ron Swanson