But we do influence how effectively L1/L2 caches are used. Each time we have a choice to split some fields into two objects or not, they can be allocated/cached

But we do influence how effectively L1/L2 caches are used. Each time we have a choice to split some fields into two objects or not, they can be allocated/cached together or separately. This is one of the huge outcomes of Java's project Valhalla to have Value objects that live 'in-place' rather than separately, the way embedded structs do in Go.