As flash is obtrusive, blinding and high-intensity strobes are certainly not conducive to shoot intimacy and candid moments and document the unadulterated story of the wedding day. Still, the fact remains that some flash is needed and whenever you use it, you are sure to create some sort of distraction. So you must definitely draw the line, and minimize distraction wherever possible; but, how and when?

The experienced professional wedding photographers never use it during the ceremonies and rarely during the getting ready period so that they can avoid distractions. But the worst time for them to use flash is when they are in close contact with people. They can thus minimize the number of flashes going off in those situations. They usually avoid flash even during getting ready shots, unless the room is very dark or lacks any ambient light aside from overhead fluorescents, whereas skilled photographers use the flash almost the whole time during receptions. However, even then they prefer to dial down their bounced flash and mix it with a lot of ambient light that will generally less distract the guests than heavy doses of direct flash.

ENHANCING THE IMAGE FURTHER : The enhanced control afforded by on-camera flash is often extended from simply correcting poor light situations to actually enhancing the atmosphere of the image, at the same time sticking to documenting reality Most professionals make frequent use of shutter drag, lengthening the time of exposure just enough such that the available light registers on the image while using the flash to fill out the scene. This technique goes very well with exposing the main subject perfectly while better illuminating background details, particularly in dim light situations. And, you may let your creativity go from there.
An expert photographer often drags the shutter or zooms with the flash so that the main subject is sharp but the background might be a little dim. With a shutter speed, say, a fifth of a second or slower if you start zooming you will get a nice effect there. You have to be cautious not to overdue it, but it could be very interesting to experiment.

This enhancement of images also could be achieved by using second shutter sync and a slow shutter speed to create a sense of motion. You set the shutter speed and the aperture to about 1.5 to 2 stops under the ambient light and set the flash to expose for ambient light. You then pan the camera and zoom the lens to create a blurry background while the subject is bathed by the flash.

The unflattering backlighting seems very suitable for taking pictures of best man/maid of honor toasts, as venues love to set up the head tables directly in front of a wall of windows. Even though many lighting deficiencies can be corrected in post-production, but not worth since tweaking images in Photoshop consumes more time, means more money.