What is the strategic purpose of separating the DSN stations (Goldstone, Madrid, Canberra)?

To ensure at least one station always has a clear line of sight to Mars due to Earth's rotation.

The Deep Space Network (DSN) maintains three primary complexes situated roughly 120 degrees apart in longitude around the globe: Goldstone in California, Madrid in Spain, and Canberra in Australia. This precise geographical distribution is fundamental to maintaining continuous communication links with Mars missions. Since the Earth is constantly rotating, this global placement guarantees that as one station passes out of range or loses line of sight with Mars due to the planet's rotation, another station positioned on the opposite side of the globe simultaneously rotates into optimal alignment. This setup ensures near-continuous reception capability for tracking, commanding, and receiving vital data packages.