If you are going to orbit, you need enough kinetic energy to stay in orbit along every point of the orbit. If it's a polar orbit, it covers every latitude, from

If you are going to orbit, you need enough kinetic energy to stay in orbit along every point of the orbit. If it's a polar orbit, it covers every latitude, from north pole to equator to south pole. The real advantage of launching from a pole, if you are going to a polar orbit, is that you don't start out with a velocity component due to Earth's rotation, i.e. perpendicular to where want to go. If you do, you'll have to spend part of your fuel budget canceling out that unwanted velocity component. On the other hand, if you're going into an equatorial orbit (e.g. a geosynchronous one) you want to pick up as much of that free contribution from Earth's rotation as possible, so you pick a launch site on the equator, or as close to it as you can go. Polar and equatorial orbits are opposite edge cases. In general, your orbit will be at some angle to the equator, and the closer that angle gets to 90 degrees, the closer to a pole you'll want to go for optimal launch latitude. BTW, surface gravity is lower at the equator (9.78 m/s^2) than at the poles (9.81 m/s^2), exactly because of Earth's rotation.