It might be useful. The Lion optimizer uses 1-bit values to represent forward or backward. NNs can pick up on patterns like that in very strange ways. Of course, those are 1's, not 0's, so maybe the benefit disappears when multiplying by zero. But it's important to challenge assumptions like "well, let's get rid of the negative half of 0" before you test experimentally whether it's useful or not. NNs are nothing if not shockingly weird when you try to make them.