This 2-ILS hub is for a specific type of gameplay- if you are importing raw ingredients from another planet or system, and want them sprayed with proliferator before distribution across the planet. Think of it as a planetary customs office.
The first hub (labeled Planetary Intake Hub): - Imports up to 4 ingredients from off-world - sends them down 3 belts apiece (except for item #4, which only has 2 belts- so use that slot for lower-throughput items) - pushes them through sprayers across to the second hub - has an intake behind it if you like to run warpers to your ILS using belts instead of logistics drones
The second hub (labeled Planetary Distribution Hub): - takes the now-sprayed ingredients and distributes them on that planet only - is the storehouse of proliferator for the sprayers. Set by default to blue (Mk III) Proliferator, easily changed.
Advantages: - You can use more compact hub designs; you no longer have to add sprayers on ingredient lines, but just on the output line. - Easier to manage importing of offworld ingredients; place one or more of these right by each other and you can easily check them at a glance.
Disadvantages: - Makes a choke point for high-volume imports; may need multiples of these hubs for some high-demand ingredients.