Why 16 bits

16 bit pixel depth is the preferred way of archiving high quality
scans. While images scanned in 16 bits doubles the size of the
file, it also provides you with 65,536 levels of grey versus 256
with 8 bits.

The main advantage that accompanies 16 bits is the ability to
enhance detail throughout the tonal range. The Photoshop feature
that works best is the pencil tool in curves. Simply move the cursor
along the curve to identify the regions in the image that need en-
hancement. Try out different concave and convex curve re-
shapes and observe how it brings out greater detail.

With such an abundance of levels to work with, there is virtually
no risk of posterization which can occur in 8 bits and which shows
up as gaps in the histogram.