When you enter a date, a time or a date + time in your sheet, Google Sheets will recognize this format and automatically apply the right format to that cell. Read more here.
The Data Editor will also recognize this format and automatically assign a Date/Time Column type.
When the Data Editor recognizes a column as a date, a time or a date + time you get access to the Date/Time formatting settings.
This can be very useful if the dates & times in your sheet are in a different format to that which you want to display in your app.