Isn't the larger point here that these larger units solve micromanagement problems without impacting the finished product? If not, then why stop at hours? Why

Isn't the larger point here that these larger units solve micromanagement problems without impacting the finished product? If not, then why stop at hours? Why not bill by the minute or second? The answer to why hours are superior to minutes is the same as why days are superior to hours. It's just a useful level of aggregation to mitigate tedium.