More concrete...

It all depends on what the local codes require. Around here flatwork, except sidewalks, require #4 bar on 2' centers as a minimum. Foundations for a building is another whole story. Contractors don't like fiber as it is darn near impossible to get a slick finish with all the hair sticking up. But long term, the fibers break off and aren't a problem. OR, if you are impatient, a floor buffer with a scrubbing disc makes short work of them.