I thought baked wares which include baking soda should be put into oven immediately, otherwise they won't rise. But some cookie recipes call for cooling the dough in the fridge or even freezing it, which seems would negative the leavening properties of soda. Does it have other purpose or could it be left out?
Baking soda also raises the PH of the product resulting in better browning.
Soda can be left out. Many recipes- especially for chewier cookies- don't call for any leavening besides the eggs. http://www.foodnetwork.com/recipes/alton-brown/the-chewy-recipe/index.html
Cookie recipes often call for the dough to be chilled so that it spreads less in the oven before it sets. This creates a taller, less crispy cookie. Cookie recipes don't typically have very much water in them for the soda to dissolve into. Much of the water is tied up in the butter and won't be available until the dough melts in the oven.