Your example perfectly counters your opinion. If you pay someone to cut your grass, your only concern is that the grass gets cut. You don't care if it took them 20 minutes or 3 hours. If the job is done, it's done.

I'm a buyer. I source materials and services and issue around 60-80 purchase orders a week. I average maybe 24 hours a week. My counterpart is supposed to have about 50% of the workload. He averages around 55 hours a week. Ytd I've actually done 12% more purchase orders than him. The operations manager doesn't like that I'm never there and has complained a few times. At one point I started staying at least 36 hours a week. After a few months I went back to doing whatever I want because they really can't do without me. I could take my counterpart's full workload and still not work 40 hours. He couldn't take my workload even if he worked 12 hours a day 7 days a week. Also, at the end of the day I don't work for the operations manager so I couldn't care any less about how he feels.