It’s a simple ‘supply’ and ‘demand’ analogy. Imagine walking into a store that sells heaters in the middle of winter or an air cooling fan shop in the middle of summer. The prices of the goods/services will reflect the demand at the time. So both items are likely to cost a lot more when the demand is high. If however, you were to purchase the same product when demand was low, you would get a far better deal.
In relation to photography and videography the best deals are made when demand is low. In my experience December and January are the best times to buy for summer weddings. On average couples save around £350/£400 pounds by planning in advanced. If you’ve got your dates and location that’s all you need to get a quote. Most suppliers will have the time and space to devote their attention to your needs and budget if there is plenty of time before your event. During peak season, however, the same supplier may not be as flexible with time as the demand will be high and there will be little or no time for meetings.