I will be travelling in Switzerland, and I am planning to leave my passport in the hotel. How often are random passport/visa checks in Swiss trains? Thank you in advance.
It sometimes happens near borders (for example on the Zurich-Milan train, I was once checked between Lugano and Chiasso, both in Switzerland), but it's not a general phenomenon.
So if you want, you can keep your passport at the hotel, but do carry a laminated copy just in case (ID page and, if applicable, pages with the entry stamp and visa)
Please be careful when it comes to making copies of official documents. They may be considered an attempt to counterfeit.
In Switzerland you are not required to carry any ID with you. But practically, this may make you loose some time if a policeman thinks he / she has a reason to check your identity.
Any other official document issued by your home country; preferably with a picture on it (driving license?) may serve as a replacement ID.