Attempt to fill your loot box slots as quick as possible, since that's where you will get your resources and cards for upgrading your Pins from-- so the more you have and the quicker you get them, the more powerful your deck will be. It does not make much sense to play the game once your slots are filled, unless you wish to practice and enhance your game. Rather, take a time-out from Gears Pop, await the time to pass so that you can get those boxes unlocked and play once again to fill empty slots. At the same time, concentrate on the Tactical Challenges for some fast rewards.