When doing eastbound launches the rotation of the Earth gives you some free starting velocity. This free velocity is higher the closer you are to the equator. A

When doing eastbound launches the rotation of the Earth gives you some free starting velocity. This free velocity is higher the closer you are to the equator. Also helpful in eastward launches is ocean to the east of the launch site. If something goes wrong and your rocket crashes the debris is likely to hit uninhabited water rather than a suburb. The bonus velocity you get for launching further south can end up increasing payload mass by significant percentages or giving a smaller mass more velocity to achieve higher orbits with the same amount of fuel.