In general, the cameras are configured to meter a scene using the evaluative meter settings. However, that doesn’t mean that you have to stick to that setting all the time; there are three settings to consider. The purpose of the evaluative settings is to analyze the whole scene and create the best possible scene to make a scene through camera.
Center-weighted metering is another option; it meters a scene based determining what is in the middle of the camera’s view.
Spot metering, on the other hand, meters a scene determining a spot you decide. Obviously, spot metering is best used with a manual autofocus point selection.
Interestingly, most of the people don’t consider about the metering mode when shooting. They just consider what appears on the LCD screen. If the image doesn’t come up nicely, they just try to change the exposure.
If you have a specific subject in the scene to focus, you should use spot metering instead of relying on the default evaluative meter settings. Particularly, when it comes to portraiture, you have to use spot metering technique. When it comes to a landscape, however, evaluative metering will do the best in most of the cases.