The ability of the rope to resist wet conditions and dirt, dust, etc. is what makes it different from a non-dry one. While it is recommended that you purchase a climbing rope with a dry finish for safety reasons, this may not be necessary. It does reduce the risk of possible harm in bad weather, but you don't need it if your plans are to not use your rope under such circumstances. For example, gym climbing does not need a dry rope. The same applies for sunny or cloudy weather. If you have a rope that is not going to get too heavy due to water absorption, then feel free choose the dry rope.