The demand and capacity buffer allows end users to understand the capacity required if:
1. They wanted to treat patients 2 weeks prior to their treat by date (2 weeks)
2. They wanted to treat all patients one week prior to their treat by date (1 week)
3. They wanted to treat everyone the week of their treat by date (0 weeks)
The component defaults to 2 weeks as it assumes there is too great a risk of people becoming overdue if we plan to treat everyone on the week they are due, because of unavoidable hospital initiated cancellations.