Here's my 2 cents:
If I was limited to one unit only, then I'd place it
in the location for the type of fishing I normally do
the most and just leave it there.
Continually unhooking and hooking up and moving a unit is a receipe
for something to go wrong (dropping it, bending/loose connectors).
Also, while on the water, moving the unit back and forth will get old real fast.
If you want to be versatile and use a bow mounted and
a transom mounted transducer, then I'd get two units
and link them together so the waypoints can be
shared.