Originally Posted by DiapDealer
In my experience, the subject metadata (and any of the metadata, really) that is internal to the epub is not even used by most online retailers or seen by potential customers/readers. Not directly anyway.
They're used by libraries, and by certain distributors. If you're trying to reach readers, use text, not BISAC codes. If you're trying to get to libraries, use BISAC codes.
However, the reality is: it can't hurt to use it, but the BISCAC codes won't help you with readers. When was the last time you searched for a book using a BISAC? Right? So, if you don't, most won't.