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To give you an example, my instances of MyAlbum have that option turned to 'On' so that users can submit reports of their lost or found dogs without always having a digital picture of them (this is especially true for someone who has found a dog). If they haven't gone one available they can still generate the report, and then I will add my own graphic of 'Picture Not Available' later on, rather than leaving it as a blank space.
To be honest, I expect instances like mine are the only one's when this option would be useful. In 99% of cases a webmaster is using that module because he wants his users to submit pictures!