Why should I collect all the collectible trading cards?

Question

All around town I've been picking up little scraps of cardstock with a variety of pictures on them. These "trading cards" don't seem to have an obvious reason to exist. Here are just a few I've found:

• "Emily"
• "Willie"
• A "Shadow" and an "Armed Shadow"
• A "Turkey Sandwich"
• "Ushah" and "Ushah's Chips"
• "Gina's Sponge" (whatever that means)
• Many others

What the heck are these for? Do they serve an individual or collective purpose? Do people want them? Am I just supposed look in my pockets once in awhile and admire my vast collection?

Answer 1

The cards do not have any in-game function, aside from providing some background information about people and things in Greenvale.

There is also an achievement that can be obtained when you find all 65 of them.

http://shshatteredmemories.com/greenvale/trading-cards