For example:
0) Start with an album that has some track titles that differ from what MB has.
1) Load the entire album into Picard with the intent of not having it correct any of the song titles.
2) Select all tracks.
3) In the tag list at the bottom, right click to select "Use Original Value"

RESULT: The option isn't available in the contextual menu. It only appears when a single track is selected.

This is actually feature regression: previous version of Picard were capable of doing this, albeit in a roundabout way:
1) Select the files.
2) Get info.
3) Delete the tag you didn't want updated.
RESULT: Picard would just ignore that tag and not edit it. In 1.0, if you select "Remove", it actually removes the entire tag from the file (regardless of whether or not changes were to be made to it).