Interestingly, one of the best uses of your flash is during bright sunlight! I know it sounds strange but it’s true.
A flash helps to eliminate dark shadows (for instance under the eyes and chin of faces). It also helps to emphasize your subject.
When you take pictures of subjects with bright light behind them, for example a portrait that is backlit, or a duck swimming in water reflecting the sun, the camera will be fooled by the bright surroundings so the subject appears dark.
By turning flash on, you will fill in the shadow areas making the picture much more pleasing.
It can also be used to add a sparkle to eyes, and to reduce shadows under the nose and eyes when pictures are taken when the sun is bright and high in the sky (eg at midday).
Nature photographers even use flash to ensure the nooks and crannies of flower petals are properly lit – to reduce shadows.
Professional photographers use flash much more often than amateurs.