From: Bratislava, Slovakia
The standard CVEs (capacity of around 30, speed 20+) can be used with some effect as a support force for the KB - providing CAP, ASW and NavS freeing the strike force for their main mission. Having Tayio, Chuyo, Unyo, Kaiyo, Shinyo and even Hosho can boost your Fighter complement by about 150+ fighters - with smaller air wings fielded by main KB carriers I find this useful, especially once the allied carriers got their VF squadrons resized to 36. I usually keep the CVEs in their own Task Force (or maybe pair them with Junyo, Hiyo or CVLs).
The price is slowing down of the whole fleet and vulnerability of those CVEs. But you rather loose a CVE than CV or no?
Army CVEs (capacity of around 8) falls to another category. At first I thought about building them for the important convoy escorts serving as ASW carriers. But given the price in terms of HI to build them and their PP worth, I stopped them all. You do not have the Merchant Shipyards and HI points to spare - I would rather have some Escorts and number of planes build up. So far Allied subs in my Jap PBEM are more of nuisance than serious threat (April 1943).