How does "cache dates" work?
Found this 5 year old comment in the issue thread that gives some more context. Not sure why the enhanced help text didn't make it into the 7.x module, but it helped me make the decision. https://www.drupal.org/project/date/issues/1358790#comment-6327490


  In order to display a date, a date object is created. Creating and caching date objects at the time date field data is entered may improve performance. For single-value, non-repeating, date fields caching will be neutral or have a performance benefit. For multiple-value or repeating dates with a large number of values, caching may negatively impact performance as some date objects that are cached may never actually be required.