Sentence fragments are often used to make writing sound conversational, as in this Facebook status update:
Realizing that there are no edible bagels in this part of Oregon. Sigh.
Fragments—groups of words that are punctuated as sentences but are not sentences—are often seen in intentionally informal writing and in public writing, such as advertising, that aims to attract attention or give a phrase special emphasis. But you should think carefully before using fragments in academic or professional writing, where readers might regard them as errors.