What is the role of the minuscule temperature variations, known as anisotropies, in the CMB?

They represent the slight density fluctuations that eventually seeded all cosmic structures.

While the overall temperature of the CMB is nearly perfect, the slight differences—the anisotropies—are immensely significant scientifically. These minuscule fluctuations, measured in microkelvins, represent regions in the early universe's plasma soup that were infinitesimally denser or less dense than the average. These slight variations in density served as the initial conditions or seeds. Over billions of years, gravitational attraction caused the denser regions to collapse and aggregate, ultimately growing into all the large-scale structures observed today, including galaxies, clusters, and the filaments and voids.