For example, Marvel Super Heroes Collector Boosters can contain cards from the main set, the bonus sheet, the Commander precons, the Jumpstart Boosters, and the Scene Boxes
it won't, of course, be alone in your lists
The Barcode is the only of these 3 to also use the Thin Black Border instead of the Thick/Standard ones
You might not have an urgent need for a specific card on turns 2-4, so rather than potentially wasting a tutor on a card that could be rendered useless as the game develops, you can simply set yourself up to make a more informed decision later
The second number is the number of cards in that set
If your opponent sideboards out a lot of his or her creature removal while you sideboard in a number of threatening creatures, you might be able to steal an easy win