The Galaxy Cauldron is the source of all life in this galaxy. Every starseed in the galaxy emerged from Galaxy Cauldron, and eventually every starseed returns to Galaxy Cauldron; it is a holy place to all Sailor Senshi, and a source of unimaginable power running so deep and strong as to be a powerful, ultimately fatal, lure for those who would take advantage of its limitless strength.
The Cauldron in Sailor Moon
Galaxy Cauldron played host to the court of the corrupted Sailor Galaxia, and served neatly as a base of operations for the powerful Chaos-tainted senshi as the source of all starseeds, and thus the source of all Sailor Crystals. She would have instant access to any interesting sailor crystals that emerged from the cauldron, and her own personal teleportation skills allowed her to travel instantaneously to any location she desired.
The Cauldron in Suburban Senshi
After Galaxia's first defeat at Sailor Moon's hands, the sailor senshi who found themselves reincarnated also generally found themselves without a planet to protect. Many of these upstanding souls banded together to form the Sailor Corps and constructed their base of operations orbiting Galaxy Cauldron.