studying film and working on some small projects for clients and myself
dps have a multi faceted role.
they're [normally] the camera and lighting expert
they should understand how to evoke emotion with the image (composition and lighting)
on smaller sets they could also be operating the equipment
in most cases the director doesn't know how to create emotion and mood with the composition, framing or lighting of the shot and without a dp would be left without a leg to stand on
on some smaller shoots they director may have former experience has a dp or understand the role enough and so combine the roles together.