What is the purpose of allowing the piped Macaron batter to dry before baking?

Allowing piped macaron batter to dry before baking primarily serves to prevent spreading. During this drying period, a film forms on the surface of the batter, which helps maintain the shape of the macaron as they bake. Without this drying step, the batter lacks structure and may spread out during the baking process, resulting in flat, misshapen cookies that do not develop the characteristic smooth top and frilly "feet" that are desirable in macarons.

While enhanced color, a smoother surface, and air incorporation are relevant aspects of macaron making, they are not the primary reasons for the drying step. The formation of a skin on the surface of the macaron is critical for achieving the right texture and preventing unwanted spreading during baking, thus ensuring the end product is well-formed and aesthetically pleasing.