I'll add another possibility to @Imre's excellent list: full-image blur can give impressions of disconnectedness, loneliness, mental haze, etc. All of these are potential emotions that you wish to convey. 

Why would one shoot a fully blurred picture?
This question brings up an important question:

Do we want to allow or avoid the use of non-standard English such as the words zie and zir as non gender specific pronouns on this site?
