Transports are acceptable losses in naval battles, that came up a couple of days ago on this board.
As far as strategy of moving TRNs unescorted or taking or not taking them with you in a big naval battle that is highly sitiuational. First off TRNs still have no attack value so moving them into combat without escort is suicide. The US and Japan early on might have the luxury of moving TRNs unescorted. In the US case particularly from Hawii to New Britain and back. Usually your warships are in New Britain.
As far as just bringing them for fodder you don’t really have that luxury. Managing your logistics is a big part of Pacific. The US doesn’t have time to make attacks without assaulting the islands. You don’t have time to build and re-build and move across the ocean the TRNs you need to get those Marines (who do cost four, Marine and an ART are a great deal in Pacific IMO more punch less cost a 3 and a 2 vs a 3 and 1 for ARM, INF or 2,2 for INF, ART.)
You can use TRNs as fodder but you really won’t want to.