Why was the Aquilo Island map generator resource added?

Aquilo map generation works a little differently: islands are placed wherever resources are generated.
So if the No resources preset is selected, no islands will be created on Aquilo.
This resource setting will generate islands without resources, producing vanilla-like map generation.

What effect will it have with other map presets?

If active and left at its default settings, it will generate a few empty islands on Aquilo.
You can experiment with the setting in the Map Generator using the Preview option.

Note: The Richness slider has no effect.