The fundamental difference between anodized aluminum and non-anodized aluminum is that the former has a layer of oxide over the surface, whereas the latter does not. From a practical standpoint, anodized aluminum offers several benefits. The main benefit of anodized aluminum is greater protection from corrosion. Aluminum, whether anodized or not, isn’t susceptible to rust. Even when left outdoors under the rain, aluminum will never rust because it doesn’t contain any iron. Nonetheless, it can still corrode, and this is why anodizing comes handy for protection against corrosions. The layer of oxide this process forms over aluminum creates a barrier of protection that discourages corrosion. Also, anodizing can be used for dying aluminum surfaces. Dyes can be added to the acid bath in which aluminum is exposed to achieve different colors. There are other ways to dye aluminum, but anodizing creates a stronger bond since the dye is located in the oxide layer covering the surface.

Figure 1. Anodizing pores, Hydrate film, and Dye interaction during anodizing process

Anodizing treated aluminum products have much higher corrosion resistance, maintaining its strength and colors under weather impacts.
Figure 2. Anodizing treated aluminum surface under weather impact   

As you see on left, Non-anodizing treated aluminum surface is much more susceptible for corrosion, degrading the strength and changing appearance of the aluminum surface.
Figure 3. Non-anodizing treated aluminum surface under weather impact