For some jobs (e.g., assembly-line work, or being a receptionist), every hour that the employee is on the clock adds value to the company. For all other jobs,

For some jobs (e.g., assembly-line work, or being a receptionist), every hour that the employee is on the clock adds value to the company. For all other jobs, I don't think any rule of "you are expected to work X hours per day", whether X is 8 or 6, is really useful. At the end of the day, er, performance-review period, either you've created value for your employer that justifies the salary they paid you, or you haven't. If you did, why should the employer care whether you did the job in 6, 8, or 10 hours per day? If you didn't, then some kind of remedial action needs to be taken, and the action is not necessarily "do what you were doing before, but for more hours". And if the employer can't gauge the value of an employee's contribution without referring to how many hours per week the employee showed up, then the employer has bigger problems.