Capacity is usually counted in appointments. Counting it in hours is what makes it answerable.
Why it matters
“Can we take on 200 more accounts” has no answer in jobs, because jobs differ in length and in distance. In hours it becomes arithmetic: committed service time, plus the drive time that serving it implies, against the hours the calendar really contains.
The drive portion is the part people forget, and it is the part that moves. The same 200 accounts might need two technicians if they cluster and three if they scatter. That is a routing decision shaping a hiring decision.
How you notice it slipping
Capacity is discussed as a feeling — the schedule looks full. Overtime rises before anybody says the word capacity. New business is accepted and then placed wherever there is a gap, which is the moment density is given away.
What to do
Express it as committed hours against available hours, per week, per territory. Then watch the trend rather than the level. A territory moving from 80% to 95% over a quarter will produce overtime long before it produces a decision, unless somebody is reading the slope.