Payroll is the largest expense for many businesses, so planning it at the level of individual roles gives much better forecasts than a single payroll line. A headcount plan lists current and planned positions, start or end dates, salary or wage assumptions, and the loaded costs of taxes and benefits.
Headcount plans make hiring decisions concrete. Moving a start date from March to June, or comparing a full-time hire with overtime, shows up directly in operating costs and cash. Because compensation data is sensitive, access to the headcount plan is usually restricted more tightly than the rest of the forecast.