Public holiday

Hi, I hope someone can help me. I have a client who ask: Why do we have public Holidays in the calender in SAP. What is the purpose of this?

and ask would it be possible to remove public Holidays in SAP, snf what will the risk be for the rest of the calculations in the system.

I think it's a big question - can someone give me a short input till an answeer ?

Thank You in advance.