Upon hitting certain level of upgrades, Maker will receive a bonus. You can choose how much you want to upgrade your makers, either 1 or maximum levels you can afford.
Some of the first Maker quota bonus milestones: Level 25-50-100.
At these milestones, you will earn not only profit bonus for the maker but also one of the following rewards Cow coins/Character cards/Maker cards.
Once you reach a milestone you will see a profit multiplier apply to that Maker, and an amount of Cow coins and/or Cards you earned showing up above the Maker.
The level bar shows how many levels left until the next bonus.
If the upgrade level is full, indicating with MAX next to it, it means you have reached the maximum bonus for the maker, it's time to work on another maker. Additionally, you can still upgrade your makers but you won't receive any Coins or Cards.