The effective period defines the active or inactive date range for a schedule (weekly and exception schedule) using the date range rules. In Edit mode, the Browse icon opens the Effective Period dialog box. By default, a schedule is always active.
For example, you can create two schedules with the same items/objects and configure one for the heating season and the other for the cooling season. Then you can define the effective period of the heating schedule from October through March and the cooling schedule from April through September of each year.