sfarson has it exactly right... they're complementry... not either or... my GPS I use to track my speed, time to destination, time to next stop (usually put that as a gas station) trip od, total od, and current time...
I use the map to actually find my way... durring the day... that is.
at night... I flip my GPS back to map mode... cause I can just glance and see what I need... instead of turning on a map light... or on my bike... stopping and finding a flash light