Fiberglass will decrease concrete surface cracking and its increase the overall tensile strength of concrete. Fiberglass WILL NOT replace steel wire or steel rod in structural concrete.

You can get away with only fiber-glass in a patio or a sidewalk, but even in a driveway you are pushing your luck.

In a concrete structural slab you can replace the wire mesh with fiber-glass, but the steel bar is still required in this, assuming you are using both in this concrete.