Gravity is a conservative force.
That means that when you move around in a gravitational field,
the amount of energy you need in order to get someplace
depends only on where you start and where you finish, and
it's not affected by the route you take to get there.
Friction ... as an example ... is not like that. If friction is present and
you wander around on the way from 'A' to 'B', taking a longer route,
then you'll need more energy than you would need for a more direct,
shorter route.
