You can assign resources at less than 100% to indicate that the resource doesn't generate the 10 hours of work per day - there are other things that take away from the "productive" time.
For example, you have a task that has a work budget of 50 hours - original duration 5 -10 hour days. But during a given week (5 days) the resource can only 8 hours of work per day. So in a duration of 50 hours, the resource can only generate 80% or 40 hours of work. If the task really is 50 hours of work, the duration will be 6.25 days.