As per :faq61:, The Daily Deviation is a daily feature chosen from galleries here on deviantART.
A small assortment of submissions are chosen each day by a select group of staff/volunteer members who wish to showcase an image which they found impressive or otherwise interesting enough to deserve being brought to the attention of the community-at-large.
Benefits of suggesting Daily Deviations:
helping artists gain more exposure
deviantART is such a large website with many members, often great art can fall through the cracks and go unnoticed as a result. Daily Deviations are usually a wonderful way to put a bit of a spotlight on a particular piece or artist. Often people like to focus on the lesser known artists, though it may be worth noting that even deviations uploaded by popular artists can at times use more exposure as well