If we assume that humanity is the result of directed development by an intelligent designer and is the only life in the universe, the question of whether multiple galaxies were necessary or if just the Milky Way would have sufficed is a matter of speculation and subjective interpretation.
However, I can explore some hypothetical perspectives:
Efficiency and Purpose: If the intelligent designer had a specific purpose in creating humanity, and the Milky Way provided all the necessary conditions and resources for that purpose, it might be argued that multiple galaxies were not necessary. An intelligent designer, being omnipotent, could potentially create a universe tailored to their intentions in a way that one galaxy would be enough.
Diversity and Complexity: On the other hand, if the designer aimed for diversity and complexity, multiple galaxies might have been created to accommodate different environments and life forms. Different galaxies could host unique conditions, star systems, and planetary arrangements, allowing for a broader range of life forms and experiences.
Cosmic Tapestry: Some proponents of the idea of an intelligent designer might argue that creating multiple galaxies serves as a cosmic tapestry, demonstrating the vastness of creation and the magnificence of the designer's abilities.
Unknown Purpose: It is also possible that the reasons for creating multiple galaxies, assuming they exist, could be beyond our comprehension. An intelligent designer with capabilities far beyond human understanding might have motivations and objectives that we cannot fathom.
Ultimately, the question delves into philosophical and theological territory, and opinions on this matter can differ widely depending on individual beliefs, religious views, and worldviews. As such, there is no definitive answer, and it remains a topic of speculation and personal interpretation.