In your Informant Settings > General Settings you'll see an option to toggle on/off SmartTitle Autocomplete.

This option allows you to start typing a Contact from your Contact list into your Title field and SmartTitle will fill in that Contact for you. (This does not, however, add that contact as an attendee in your event. You will still have to add that Contact as an attendee in the attendee field.)

You can also use SmartTitle Autocomplete in your Location field. Simply start typing in the name of a Location and Informant will bring up a list of all of those locations starting with the closest to you.