Is it really a thing? How is it different from the overall traditional photography?
A candid photograph portrays the natural pose of your subject experiencing their immediate environment. While the subject may or may not be aware of their involvement in your frame, they definitely do not pose for the frame. Most of the time when a photographer is out on the streets to shoot random subjects/people it is not possible to request them to pose all the time. So what you do is patiently wait for the best shot to compose itself and when it appears (and it will) you capture it. Of course, manners dictates that you inform the person if they were unaware of their picture being taken. Remember, there is a fine line between candid photography and creepy behaviour.
The principle of candid photography can also be applied for wedding photography. It will enable you to shoot true emotions, raw and whole. Of course, to get the best ones you must be on your toes at all times; alert and vigilant to capture a beautiful moment as it unfolds. This will involve moving around the area a fair bit and experimenting with different angles and potential subjects. That way, you are likely to capture some truly heart-warming moments and create indelible memories for everyone involved. A good-looking candid usually speaks beyond what its subject feels. It highlights the general mood of the event and, if portrayed right, could bring a lot of positive vibes for the album. At Indian weddings a lot of things happen at the speed of light. To capture it all, the candid photographer has to be quick on their feet. Sometimes, moving a few feet in another direction can work wonders for frame composition.
To master candids, you must know everything about your camera and lenses; its advantages and limitations. To start off, you may use my favourite setting for candid photography. I set the aperture to its widest opening (f1.4 to f2.8) and keep the shutter speed at 1/100 to 1/125 of a second while letting the camera decide the ISO needed for perfect exposure. These settings ensure that I am able to capture every detail without compromising on the sharpness of the image.
Pro tip: Carry two cameras (if possible) with two different lenses (one telescopic and one prime/wide zoom). By equipping each body with a lens each, I work around the cumbersome task of frequently switching lenses on one camera body. I prefer carrying my 5D Mark IV with 70-200 and 6D Mark II with 24-70 and I keep my 85 mm in my pocket all the time just in case. You never know when the perfect moment is waiting to unfold. It helps to be prepared. Trust me, I know.