You'll get a ton of stubs for finishing off positional players (created players collection) (siver/gold respectively) as well as the starter collection, and the live series collections.
I wound up with about 70+ thousand stubs for just adding them to each of those collections. Only add the diamonds you have if you do not plan to sell them. Going through those, and then adding each team the cards for them respectively, after hitting certain numeric thresholds, you'll receive stubs too.
All of the above will also add XP to your profile, helping to get your level up and the rewards received for hitting every 5 levels. I just passed level 50, which will reward you with a diamond player of your choosing... They show about 20 cards from which to choose.
It's a definite way to increase your ability to buy packs, or players depending on your preference. Well worth the small amount of time it takes to add players.