Star Fragments

Benefits
Once you get to 10 Stars, you will be able to get Star Fragments. You can use Star Fragments to level up your Stars, increasing their multiplier.

To do that, you will have to convert barrels. The higher level the barrel, the more Star Fragments it gives you(tier/1000), upgradeable with Bricks. The amount of Star Fragments given can be increased through the 'More Fragments' upgrade, purchasable with Bricks.

For Tree Upgrades
Some Tree Upgrades (unlocked at 40+ Stars) need Star Fragments to be unlocked.

Tricks
The most efficient way of getting Star Fragments is to activate an x10 Faster Barrels Ad Event, and just keep on tapping the barrel above which the confirmation window's yes button appears. Never convert your best barrels unless you can get there quite quickly anyway.