Only paying workers for work done rather time on location has the side effect of encouraging companies to over-hire and increasing tolerance for slow work speeds due to the extra workers to pick up the slack. What you end up with is 50 guys to do the job of twenty, on site for a typical work week, yet because of only being paid for work done and not having nearly enough work for everyone most end up making less than a typical part time worker. Working fast wouldn't mean that you'd have more assigned to you unless the company actually needed to speed up production.