While capturing wedding shots outdoors, no diffusers or modifiers, no bounce is required. Here flash is used either as a slight fill to get rid of harsh shadows or with greater power to bring the subject in balance with the ambient light, usually for backlit formals. It could be very particularly useful for keeping eye sockets from getting too dark or to lower the contrast ratio of shadows and highlights in direct sun.

Useful Tips For On-Camera Flash :

Don’t use the flash to overpower the existing ambient light wherever possible, but compliment it.

You should be always well aware of your subject and what you are illuminating.

Should know what look you want to get and how to deal with your flash settings. Many photographers try and work by taking a technical setting and trying to adjust it into their style.

Bounce always while indoors to maximize the effective light on the subject, reduce fall-off and soften the light source.

The quality and direction of the flash must be generally more important than intensity of light.

Study carefully your flash and camera characteristics before you add any third party attachments.

As there is no substitute for fast lenses use them as much as possible to bring in more ambient light, thereby giving more balance between that and the flash.

Shooting Raw gives you latitude without causing any worry about color temperature.

As a whole, your aim should be use, bounce and combine the flash with ambient light. 
For slight fills, Nikon strobes at about -1 to -2 powers could be used since the Nikon TTL system is quite accurate. Balancing with sunlight is a lot tougher, as you have to meter for the ambient light, and then dial up the strobe, usually to maximum power, to properly expose the subject. Sometimes they we will take the flash off the hot-shoe outdoors and use it to mimic highlights from direct sun on otherwise overcast days that would lead to very flat lighting.

When the subject is close, and the sky is clear or partly cloudy, the photographers use high-speed sync and a fast shutter along with dialing in some negative exposure compensation to darken the background, saturate the blue in the sky and add a little change to any clouds. By leaving the flash exposure compensation neutral, the subject will be properly exposed and pop a bit more from the darker ambient background. On bright days, this requires a lot of flash power to counter daylight, so staying close to the subject, using larger apertures, and having a battery pack helps with the recycle times of the speedlights.

 Previously, on-camera flash was considered as a source of light to fill in shadows or provide lighting when there is none. However, now the photographers realize that the flashlight, depending on which direction it is falling upon the subject, can create whatever mood you want to convey in the images you are shooting.  The main advantage is that on-camera flash gives you freedom, freedom from fixed room lights and their corresponding stands and cords, radio triggers, and pre-set locations to shoot within, or freedom from having an assistant follow you around with a light stick. In very dynamic situations, you need that freedom and flexibility.