Mounts allow you to travel faster than running.
There are two types of mounts:
The primary difference, obviously, is that flying mounts allow you to fly. Elven wings count as a flying mount.
Ground mounts take up a space in your pet bag, and require food and gain loyalty like any pet. They also gain levels and grow slightly faster over time. While on a ground mount, you can single jump and run, but not attack, fly, or swim.
Flying mounts, also called 'Aerogear', use a special equipment slot. You can attack while using aerogear, although there is a damage modifier. You cannot jump or swim.
Mounts have their own movement speed - and are not affected by most runspeed improvement items, skills, or potions.
The elven 'improve flying speed' skill only affects their default wings, not any other wings they purchase.