It's required for literally any recurrent economic activity, even selling old things on classifieds sites.
That's just for basic sole-proprietor. Private limited company is much more complicated. I wouldn't dare to register it. So it doesn't exist.
This is an extremely low rate for a developed country and there are plans to make tax avoidance by limited companies even easier in 2021 by incorporating solutions from the Estonian tax system.
As a sole proprietor you pay only 16255 PLN/year for your health and social insurance. This is no matter how big your income is and what your health condition is. You could be making millions while suffering from a chronic disease and you would be still paying the same minimal amount for your insurance. There are also some ways to reduce it even further, e.g. if you are starting your first business.