Minecraft wiki entry for Best_biomes_for_homes, associated text: At this height, the player will not have much difficulty lighting up their sky base, the only place where hostile mobs could spawn and attack. Phantoms are the sole exception, spawning in the air regardless of light level, but they can be avoided by sleeping frequently.
Depending on your render distance and height, you may be able to see the surface which provides a nice aerial view.
With no land obstructions, the player can exercise complete creative freedom, and have plenty of space for any structure.
A sky base is perfect for factions or anarchy servers. With only mild protection, it could be impenetrable.