Backlight compensation brightens the subject when a scene is lit from behind, such as a person in front of a bright window or an open door. It raises exposure in the metered center of the image so the face is visible, at the cost of blowing out the background.
A camera meters the whole frame, so a bright background can pull the exposure down until the person you care about is a silhouette. Backlight compensation corrects for that specific situation.
When a scene is backlit
Windows, glass doors, loading docks and drive-through lanes are the usual offenders. The fix is a modest lift in the center of the frame, applied all the time or only during the hours when the sun sits behind the subject. It is a camera setting, not a lighting solution.
BLC, WDR and highlight compensation
Wide dynamic range captures bright and dark areas in one frame, and highlight compensation masks the glare of headlights or spotlights. Backlight compensation is the simplest of the three and the least selective. Choose wide dynamic range where the site has a contrast problem a single exposure cannot handle.