Apps like Google Calendar are great for single user appointment tracking, just like Outlook Calendar. When it comes to group calendars, it gets kludgy, with numerous workarounds required in order to get things to work the way you want to, if at all. That's where cloud calendar hosting, like KnownHost comes into the picture. Much added functionality makes this the method of choice for groups. Ownership, control of data and privacy are some of the other reasons that people choose to host their own calendars, rather than having them on some external 'free' system.