Maybe you measure how many burgers they can make in an hour. Each burger sells for $x dollars. You've now quantified how much revenue that employee generates.
But it is. Because at some point I will have my labor at maximum capacity.
And in all cases they need to produce enough over the duration of their shift to offset the cost of hiring them. Why would I employee two people to work at 50% capacity when I could just hire one?
Why hire someone for two hours when I could hire someone else for one.
Yes, there are some positions wherein I need someone there whether they're doing work or sitting around. But a business that can minimize costs can win customers so there will always be the need to measure widget output to justify the hire.
