Not all elements in a game need to have a function. You can have a mechanic that’s just fun to play around with, but serves no real purpose. You see this with the basketball pre-match in Overwatch or just using the toilet in Bioshock Infinite. And you might notice that while these don’t have any mechanic function ingame, “outgame” they help to relax you a bit or just have a laugh.
With Circles, you can ‘eat up’ the circles at the end of each level. This serves some purpose before, but that got removed at some point. Now, it doesn’t really give you any points, or play into another mechanic, it’s just there to reward the player and give them so relief. It’s just fun to pick up the circles (that before you had to avoid) and see them explode afterwards.