It may depend on the situation.
Sit.1)
A lone weak escorted Carrier gets suprised by a one or a few subs.
We may assume it will not get enough Airplanes up before it gets sunk.
Sit.2)
Enemy Subs are expected in the operating area and a DD or a few Corvetts are escorting as well.
Planes will be quicker up and serching the area for Subs.
Summary:
It will be hard for planes to search areas for Subs wich could be there.
It will be more sufficent for planes to search an area where SS def. be expected.
A lone weak guarded Carrier may not be able to afford having planes up all the time searching in wide radius for anything suspicious.
And having received a good hit by a Sub on your Carrier may not give you enough time to get any planes up in time because you are busy getting everymen off board savely.
The G40 rules are based on a good decission to have Subs and Ftr separeted in combat unless a DD is present in the battle against the SS.
It gives good balance and tactical decissions to choose your targets with SS or escort your value ships right to protect them of suprising suddenly loss.