Why are the sausage rolls placed seam side down when baking?

Sausage rolls are placed seam side down when baking for a few reasons:

* To prevent the seam from opening up: The seam is the weakest point of the pastry. When the pastry rises during baking, the seam is under pressure, and it's more likely to split open if it's facing upwards. By placing the seam down, the weight of the pastry helps keep it sealed.

* To create a crisp, golden bottom: The bottom of the sausage roll will be exposed to the hot oven air, resulting in a nice crisp and golden crust.

* For visual appeal: The smooth, golden top surface looks more appealing than a potentially cracked and uneven seam.

It's important to note that there are some pastry cooks who believe that it's not necessary to bake the sausage rolls seam side down, and they get excellent results baking them seam side up. Ultimately, it comes down to personal preference and the specific recipe you're using.