Which pricing structure actually works out better.
Prepaid bookings usually offer a lower headline rate but come with less flexibility — cancellations or changes often carry a penalty or aren't allowed at all. Pay-at-counter bookings cost more but let you cancel or adjust plans without penalty, which can be valuable for less certain travel plans.
For a firm, unlikely-to-change itinerary, prepaid usually saves money; for a trip with more moving parts, the flexibility of pay-at-counter is often worth the premium.