Exposure Compensation Function Explained

Exposure compensation is a function, found on many Nikon cameras including compacts as well as DSLRs, that lets you override the camera's automatic exposure control to lighten or darken a photo or elements in the photos.

You can lighten or darken the exposure in increments up to a number of stops. The typical basic option is + or – two stops in half or third stop steps. On most Nikon cameras this function can be accessed via the d-pad but on the Nikon Coolpix P7800 there's a dedicated exposure compensation dial found on the camera. 
 

The photo on the left is of a small black ornament first placed on a white background and then on a black background (shot on the right). A camera tries to produce an average exposure from every scene. It scrambles the tonal values and provides an exposure that would result in the scrambled tones recording at around 18% grey.  This means our white background is darkened and becomes grey and our black background lightens to become grey. In both cases that affects the ornament too.
 

With the light background we need to over expose using the + compensation (+1 was fine) and with the dark background we need to under expose using the – compensation. If you find that you don't have enough stops to play with you can switch to spot meter, manual exposure or use exposure lock to obtain a better result.

Exposure Compensation comes in handy for correcting bad exposures caused by highly reflective and light subjects such as snow and sand where the camera's exposure system would be fooled into making the shot dark.

It's also useful for spot lit subjects where the background is dark and as a result the camera would make the face too bright. Shots of subjects that are small in the frame and are brighter or darker than the background would also benefit from exposure compensation as this difference will influence the exposure.

Good points
Modern digital cameras show the affect of compensation as you adjust it so it's easy to use.
This function will improve your automatic shots if you use it wisely.
Ensures a better result in difficult exposure conditions.

Bad Points
Another control to fiddle with.
Not great for grab shots unless you prepare in advance.