En plein air (French pronunciation: [ɑ̃ plɛn ɛːʁ]), or plein air painting, is a phrase borrowed from the French equivalent meaning "open (in full) air". Painting from life outside allows artist to capture so much more than artists who work from photos. Not only can the human eye catch colors and subtleties that are lost in photos, I feel like a painting of a sunrise or sunset is more "true" because a camera captures a fraction of a second of something that can take minutes to experience.
Painting from life allows the experience of life itself to work its way into the artwork. Sometimes this is quite literal like grains of sand embedded into the wet oil of a beach painting. Sometimes it is something less tangible. For example, one day I was painting in the New Mexico desert and it was a really hot, bright day. That heat worked its way through my body into my painting and amplified the colors. Later, I sold that painting to honeymoon hikers who had been out the same day. They had worked hard in the heat (like I had) and they said my painting captured the feel of the sun in a way their cameras couldn't.
Even though plein air paintings tend to be less refined than their studio counterparts, the energy captured is undeniable, and often impossible to duplicate in the studio.