well, I had this all typed once and the internet went down!
leily is right ... the reduced clean up time is WAY worth it! Parchment can also be wiped down with a wet paper towel and re-used, or flip it over and use the backside. Depending on the cookie, I can use the same parchment 3-4 times.
When I was a kid, I always marveled at how perfectly round and what pretty bottoms the bakery cookies had. How come the ones mom made didn't look pretty like that? (well, that's a whole 'nuther thread in the Lounge area....!)
Anyway, many decades later, I found out: cookies scoops and parchment paper.
The non-sticking is not just during the taking-them-off-the-tray part. It's also a benefit during the baking process. When the dough doesn't stick to the baking sheet, it can spread easily and evenly to ensure even and consistent baking ... making for a perfect and pretty cookie.
Whatever the magic is that they add to the baking process, it is SO worth it!!