Titles are used in all business and formal situations. As well as when respect is garnered. For example, my dad remarried over 25 years ago. I was already an adult when they married. I call my stepmother's mother Mrs. Brothers. She is 94 years old and deserves that respect. First names are used on a more casual level and with those that are our equals. At work you call your boss Mr., Ms., or Mrs. But a coworker can be called by their first name.