Exactly - it is a real incentive.
Manufacturing industries spend fortunes upgrading machinery to do the job faster. But, they also spend fortunes on inefficient and unrewarding work practices. Penalising people who do the work by giving them things that lazy sods didn't complete? Result - efficient worker slows down, inefficient worker carries on not giving a crap. Rewarding people for completing ahead of time? Efficient worker has more leisure time, is more likely to keep up the effort. Inefficient worker will say "I'll have a bit of that" and increase their effort.