The horizon for forecasts that are input to the sales and operations planning (S&O0P) process should be long enough that:

The horizon for forecasts that are input to the sales and operations planning (S&OP) process should be long enough that required resources can be properly planned. The S&OP process is a cross- functional process that aligns the demand and supply plans of an organization. The S&OP process consists of several steps, such as data gathering, demand planning, supply planning, pre-S&OP meeting, executive S&OP meeting, and S&OP implementation. The output of the S&OP process is the production plan, which is a statement of the resources needed to meet the aggregate demand plan over a medium-term horizon. The production plan can be stated in different units of measure depending on the type of manufacturing environment, such as hours, units, tons, or dollars. The horizon for forecasts that are input to the S&OP process should be long enough that required resources can be properly planned, meaning that the organization can anticipate and allocate the necessary capacity, materials, labor, equipment, and facilities to meet the expected demand. The horizon for forecasts should also match the lead time for acquiring or changing the resources, as well as the planning cycle for updating the production plan.
Reference: CPIM Exam Content Manual Version 7.0, Domain 4: Plan and Manage Supply, Section 4.1: Develop Supply Plans, Subsection 4.1.2: Describe how to develop a production plan (page 36).