I agree, the benefits aren’t as clear when batches are truly independent from one another. In my case, I’m doing time series prediction where the batches are created sequentially, so carrying the hidden state over does seem more natural, as you suggested.
However, in sentence classifications, one could also argue that the hidden states capture syntactic rules that is universal in how most sentences are formed, and thus few sentences are truly “independent” from one another, so that carrying the hidden state would be beneficial. I’m sure there has to be research done to answer that.