This control group serves as an untreated comparison group during the study, but eventually goes on to receive treatment at a later date. Wait list control groups are often used when it would be unethical to deny participants access to treatment, provided the wait is still shorter than that for routine services.

In the airline industry, waitlist control is a revenue management tool used when a specific flight or booking class is fully occupied. When a passenger attempts to book a seat that is currently unavailable, they are placed on a waitlist (often coded as LL in Global Distribution Systems). This allows the airline to maintain a "backup" queue of potential revenue. As confirmed passengers cancel their reservations or fail to complete payment, waitlist control systems automatically reallocate these vacated seats to waitlisted passengers based on a priority hierarchy. This hierarchy typically favors higher fare classes, elite frequent flyer status, and the chronological order of the request. For the airline, waitlist control is a vital mechanism to ensure that aircraft depart as close to full capacity as possible, minimizing the "spoilage" of a perishable product (an empty seat) while simultaneously providing a path for high-value customers to secure a spot on a desired flight even after the initial inventory has been exhausted.