If you book via an agency which uses a GDS (Sabre, Amadeus, Travelport) the GDS not only charges the airline for the booking but for the cancellation as well. The airlines are very hot on spotting such bookings.
If you book direct with the airline hardly any of them run their own reservations computer these days and, much the same as GDS bookings, each booking costs the airline.
Now, that's the basics, in the end the commercial agreement can change things but dummy bookings cost airlines money.
What does that mean for fares? It depends very much on how sophisticated the yield control system is.