Why is there a fan in the oven?
Convection in the oven is a very convenient function - hot air is evenly distributed, so you can cook on two trays at once, for example, without changing their location with each other. But not all dishes are cooked with this setting; some baked goods are best cooked in the normal baking mode.
So that your pies are baked equally from all sides (it provides the same temperature in every corner).
For a more even distribution of hot air throughout the entire volume of the oven. So that the bottom does not burn and the top does not remain damp. It is possible without it, but with a fan, the baking quality will be better.