That's not a 'bit' ("Binary digIT"). It's closer to a 'trit' ("TeRnary-digIT"). Specifically, ternary digits spanning {-1, 0, 1} (rather than the usual {0, 1, 2} in a base-3 numbering system) are 'balanced ternary'. A great intro to the theoretical reasons ternary might have some promise in computing is this 2001 article from 'American Scientist', "Third Base", which quotes Knuth calling balanced-ternary "perhaps the…
How useful are -0 and 0? You could splurge on two bits per value which gives you { -1, -0, 0, 1 }
{ -1, 0, 1, 2 }
is most obvious, but it's not clear whether it's better or worse than { -1, 0, 1/2, 1 }
Maybe theoretically (if not architecturally) it would best to "split the difference" between the two and choose { -1, 0, 1/phi, phi }
or perhaps the more implementable { -1, 0, 1, 3 }
EDIT: Of course you can also go the other way, with { -1, 1 }