The Ecliptic, which is the orbital plane of the Earth, can explain some features of the Solar System. The ecliptic breaks down the orbital path of the Earth by intersecting it with the celestial equator giving the equinoxes. It also explains the variations in the seasons along with the elliptical orbit that the planet takes. Almost all of the planets are on the ecliptic, with exceptions of Pluto, and Mercury. Finally, in a historical fact, the ecliptic helped establish the Zodiac, which became the basis of the 12 month year, going as far back as the Babylonians close to three thousand years ago.
Sources and References
What is the Ecliptic Plane?
Image 1: http://ganymede.nmsu.edu/tharriso/ast110/class05.html
Planets in the Ecliptic Plane
Image 2: http://physics.uoregon.edu/~jimbrau/astr121/Notes/Chapter6.html
Odds and Ends About the Ecliptic Plane
Image: http://www.physicalgeography.net/fundamentals/6h.html (used with permission)
Nasa -The Path of the Sun, The Ecliptic: