Sometimes, artwork can be too big or too oddly shaped to fit into a flatbed scanner. Scanning an artwork in sections and piecing it together afterward is always an option, but it can be difficult if the piece can't sit flush against the scanners recessed glass at all edges. Scanners have an incredibly short focal range. If the image is raised even one millimeter off of the surface, it will become terribly out of focus. Piecing together an image, without it being time consuming, can typically produce inaccurate results compared to the real work.
For this reason, it can typically be recommended that you photograph larger artworks to get the WHOLE image, faithfully, in one go. Photographing artwork isn't like scanning an image, though. There are a lot of conditions that can greatly affect the quality result of your shot. Scanners generate their own light in a closed space. This gives you a uniform result every time. Photography, however, relies heavily on the lighting within the room, or