Talk:Tutorial:Ideal Orbits for Communication Satellites
From Kerbal Space Program Wiki
It's necessary to use more than 3 satellites to maintain line of sight between them if the planet is too large. Using greater than 3 satellites in a circular constellation can provide the advantage that all of the coverage area of the network can be kept above the planet surface and is therefore potentially useful. The network from such a constellation reaches slightly deeper into space, so could be preferable early in the game when antenna communication range can limit mission possibilities.