The closer the observatory is to the equator, the more of the sky that telescope can view. That's usually a bonus, because then it's can be more versatile.
Light pollution is a huge factor. Light pollution will destroy images and not a lot can be done to cancel out the effects of light pollution.
Temperature plays effect as well because of image distortion from heat, but these distortions can often be cancelled out, thus temperature places little to no effect on where a telescope will be placed.