If you’ve checked your tax report you might have noticed that you are paying some money to the church of your faith (roman-catholic or protestant). The canton is billing you based on whatever you mentioned when you settled in Switzerland or as per faith you were born with.
Depending on domicile, income, wealth, children, and faith you might be paying between CHF 750 and 1400 per year. This adds up over the years!
To get those costs down you can look for “Kirchensteuer Schweiz Brief-Vorlage” and send it out or choose “konfessionslos” next time you settle in Switzerland.
Each has to make up their own mind about this step. If you want any services from the official church - you pay. Some services like marriage and funerals are organized by the local community and you get it by just paying normal taxes.
For me it was a matter of ownership. I wanted to decide as much as possible what is purchased with my money. No questions were ever asked but it could be that someone you know from your community will visit you to ask about your motivation to stop being a member of the church. Might lead to raised eyebrows in smaller and conservative communities.