Whats the usage of badges in sololearn?

Answer 1

Badges show the milestones you have been completing and each badge gets you XPs

Here is a link to a code showing the XP that each badge earns you

https://code.sololearn.com/WPWPl1tlA2fO/?ref=app

Answer 2

They let you see what your "skills" are, if you have a badge which us hard to get, everybody can see that and see that you are a more experienced coder/programmer