i'll give an example when i went to get my ICDL exams, the employer at the computer center asked me to spell my name because names can be spelt differently by different people for example sara or sarah both are correct. so when you reserve a room in a hotel by phone, the receptionist will ask you : what's your name? how do you spell it, please?

People say this in films when they are confused about the spelling of someone's name or an address.