One of the key goals of a design process is to generate as many ideas as possible and there are virtually unlimited ways in which you can modify the properties of UI elements and combine them into a design. However, designs evolve through the tunnel vision and the past experiences of the individual designer and therefore inconsistencies, no matter how small, may creep in creating a profound impact on the end-users experience.
Design Review works on the principle of achieving consistency across the organization by making every design align with the brand guidelines. Practically, Design Review feature analysis of a given design to not just identify violations but also recommend ways to make the design compliant. The decision to implement the recommendations is with the designer.