That only work if can bill your employer for all the hours you work. For example, it does not matter if I work more than 8 hours a day, I will be paid the same

That only work if can bill your employer for all the hours you work. For example, it does not matter if I work more than 8 hours a day, I will be paid the same. So if I hire somebody to wash the dishes in the evening, it is costing me money. The value I get out of it is quality of life and is difficult to quantify. Even for people running their own business on the side. Times and times again we see article on HN how IT guys can't really be more productive than a few hours a day. Also, to get back to my dish washing example - I ( and other on HN too ) noticed that that sort of repetitive work is a lot better for reflection. Replacing it with a 1 hour session playing games, working or other activities may actually be overall detrimental to your side business. What is actually useful though is to use your hourly salary to evaluate the cost of the services you buy. Like why would I expect a professional with more than 10 years experience in his field, coming to my place in the evening to work for less than 10$ a hour ?