When building a campaign to target guests who have favorited a location but never checked in at that location, make sure and build the campaign's segment using the "Guest Profile Based" attribute. If the campaign is created by Audience Type (Favorite Location), without a Guest Profile based Segment being created, it will only target guests who have checked into that location AND favorited it.
Assigning a Guest Profile Based segment ensures that guests will be targeted regardless of check in status.