lol they dont have a purpose really.
ATC's you can trade and collect like baseball cards, but for artist/crafters :D If you have a whole set (nine in a set) you can frame them. Or just stick them in a book so later you can look at them all and be inspired.
Inchies (1inch X 1inch squares) are kinda the same but they come in sets of 12. I like to frame sets of inchies and hang them by my craft table, but indivdual ones can be made into brooches, magnets, framed or just collected and saved :) They are super fun and I love seeing what other come up with!