Why is it important to keep one unfiltered view when using filters with Google Analytics?

Q: Why is it important to keep one unfiltered view when using filters with Google Analytics?

A) There is no reason to have an unfiltered view
B) In order to use a filter for multiple views
C) In order to configure Goals
D) To ensure you can always access the original data

Correct Answer is D) To ensure you can always access the original data.