Use case: I wanted to create a Course Schedule, where the user (faculty member) can select a number of Courses from a schedule.
If any of the selected courses are scheduled with conflicting dates, then an error message will be displayed to the user, indicating which of the Courses contain conflicts.

This documentation will help you get started with setting up a content type representing a "Reservation" that allows users to reserve a "Resource" using the Resource Conflict module.