Flash photography using a speedlight will give more natural
colour tones, hide shadows and bring out detail that was hiding.
A great example of what a flash can do is to fill in the
light needed if you are taking a photo of someone with light behind them, like
the sun, without flash you get a great silhouette. If you want to get the
subjects facial detail you can use fill light to do this.
Bounce flash is a great way to eliminate shadows, especially
with a wall close behind someone. Instead of the shadow falling directly behind
the subject, the flash is seemingly eliminated by changing where the shadow
falls.
By bouncing the flash on a 45 degree angle the shadow drops
closer to the ground and out of the shot. Making the photo look more 3D, give
the subject better colour tone and look more natural.