From the evolutionary perspective, there might be functional significance in the fact that qualia are private in nature and yet support our communication in the practical sense, especially in the verbal domain.
Each human being is differently composed, in terms of genetic components but also, and more importantly, in the range of experiences in the day to day lives. When several people are talking over a dinner table, for example, it might appear that they are getting more or less similar sets of sensory information. Nothing could be far from the truth. Even when sitting in the same room, the visual scene for each person is different. The miscellaneous components of the scene such as the faces of people, furniture, view from the window, the wall paper, the ceiling, etc. are differently presented to each person's mind. As the times goes by, each person will accumulate uniquely composed sets of sensory experiences and memories. Thus, after a dinner party, each person takes home different sets of sensory information.
The heterogeneity in experiences and memories become far greater when one considers the different modes of lives that each one of us lead. As we go about in the course of our daily lives, we experience and register sensory information unique to each of us. These differences accumulate over the years, resulting in quite differently composed sets of information stored in the brain.
The heterogeneity in how we look at the world can sometimes lead to misunderstandings and even conflicts. On the other hand, heterogeneity is a good thing, as we humans have a remarkable ability to share. By sharing the experiences, we can "combine" the different elements of this world as perceived and then stored in the brain's memory system. Through combination, we can generate new things. Qualia, by making elements of our phenomenal experiences accessible to the self and thus verbally reportable, support this sharing and combination process.
After a dinner party, each person takes home different sets of sensory information.