What's the purpose of parchment paper, when baking?

The parchment paper prevents whatever is being baked from sticking to the pan without adding any additional grease to the pan (also prevents from adding any additional fat calories you might not want). I would say to not use pam spray because depending on how good a pan your using, your oven, how hot you're baking, etc. the product may still stick to the pan. Parchment paper is pretty cheap and can be used for may different baking products such as cookies and brownies. I would go ahead a use parchment paper.