A two-dimensional map of a large area on Earth geometrically distorts what it is representing, while a globe, which is a sphere, can faithfully display those areas in proportion to one another. This advantage is more important when working with large areas.
A two-dimensional map is fine for representing a city, a state and even most countries. However, in order to show propoirtion correctly on a global scale, two-dimensional maps must be cut up, as with an interrupted sinusoidal map, or distorted, as with a standard Mercator projection. A globe's round shape gives students and others a realistic impression of size and distance.
Globes are not perfect for every situation. For example, the common Mercator projection map was developed because the straight lines made marine navigation easier. It is also impossible to fold a globe and put it in a pocket.