I have run into several situations when building an APP where it could save time for the submitter or prevent them having to go back and edit inconsistent information if I could auto-populate a field based on information they've entered previously.
A few examples of this
- User is prompted with a Time field labeled "Start Time" and enters 8:00 AM, a few fields further down they get another time field labeled "Completion Time". Having the default value of "Completion Time" = the Value entered in "Start Time" potentially saves the user from having to re select the Hour Value, and very likely saves them from needing to adjust AM/PM. It also provides a visual re-check on what was previously entered and might cut down on input errors.
- User is filling out a multi-screen app; on Screen 1 they fill out "Start Time" and "Finish Time". Moving onto Screen 2 they are presented with a new "Start Time" field which would default to the value of "Finish Time" from Screen 1. This has all the benefits of the previous example and additionally saves a user from having to navigate between screens to check what they have previously entered to make sure their times are matching up properly.
- A material section where a user inputs info into a number "quantity ordered" field, and you use that later as the default value of a "quantity used" or "quantity delivered" field.