I think a Bio is important in some situations where ones work is hanging in a public venue.
For example, at our gallery we have a sampling of 5 different photographers, the show consists of 7 images from each, 4 of the 5 photographers work is quite self evident to the viewer. One though is raising a bit of row, because he has included images of christ and madonna in various unflattering elements.
We opened the show without an artist statement required, and very quickly asked this paticular photographer to submit one.The statement helped the viewer understand where he was going with his imagery.
Rarely would I think a statement was necessary with ones work, but in this instance I see the value