It's amazing how a little saturation, color tint, or contrast can change the entire feeling of a photograph. In the two images above, which I shot with my iPhone 5c, shot within minutes of each other were processed through Instagram differently.
For the first I only added contrast to highlight the blue sky and puffy clouds.
For the second, the clouds began to roll in and mask the sun, so I chose "Creama" filter, with added contrast, to highlight to slightly somber tone the overcast sky created.
Filters are best used to highlight a mood, moment, or subject. So use filters to bring emphasis and focus in your photos. Just remember, a little filter goes a long way--and not every photo needs one.