It provides the following several advantages:
- Reliable route: the GPS unit will display the route exactly as intended by the cartographers. It does not rely on the map or calculation method of the device, which may be incorrect. For example:
- Some units may use car routing, taking a faster route rather than the intended slower road next to it.
- Most maps (including the current version of City Navigator) do not include off-road bicycle paths. When the route is calculated in the unit between two points, it will follow roads, not bicycle paths. Try calculating route R31101 through Burlington, VT. Yikes!
- Less cost: with full details, units with or without maps can follow the route. Maps can also be from various sources: Open Street Maps, Topo maps, City Navigator, and others. The route is already known. The map is optional for reference only.
- Compatibility: I assume not all users have Garmin with City Navigator. But that should not matter because route details are all built in. There is no need to rely on if and how the unit will calculate the route.
- More view options during trip preparation. With full route details, the route can be easily loaded and viewed on many maps & web sites. There is no need to recalculate or manipulate. It will show as intended.