A candid image is unlike either a journalistic image or a romantic portrait.
People are aware of the camera, often directed a little bit by the photographer, but it should be a quick distraction and then move on. A candid image is sometimes like a cousin of a journalistic image. But is is not a journalistic image because the strict definition of journalistic is that the subjects are not aware of the camera. It is a good opportunity for the photographer to refine an image while preserving the spirit and energy of the moment.
The candid approach works best when emotions are not profound and timing is not critical.
The technique is a bit tricky. I do like capturing candid photos, yet it's also important not to overdo them. Too many candid images stall event momentum, interfere with the bride and groom's unique story and their relationtionships, tire the bride and groom, and waste moments better that would be better as journalistic images.
A photographer should never attempt to capture candid images when they are expected to be unobtrusive, or should be.
It's often nice when I see an existing moment that can be refined and I don't feel like it would be a bother. Much depends on the serendipity of the moment, spontaneity of events, energy of the bride and groom, and available time.