As to the “never fill them” refrain... I frequently use Corvee System (or its swaps) late game... with the influence cost no longer a factor, and the energy credits being inconsequential next to your broader economy, it’s often more efficient to (mostly) depopulate conquered planets and relocate their populations to your Core, especially to ecumenopoli and ringworlds. This way, they will benefit from the +30% production from jobs thanks to your capital buildings and the +20% ecumenopolis bonus, if applicable. But either way, you’ll likely bring in more resources this way than if you just let them stay on the conquered planets, especially if they were lower-population worlds to begin with. Meanwhile, your ecumenopoli and ringworlds will be filled in no time if you keep conquering and resettling.
If you depopulate worlds in this way, you’ll have a lot of empty building slots and not many pops to work them outside of your core... so you can spam resource silos, fortresses (if you have the tradition that gives them +3 unity) or other buildings that don’t require jobs to work in order to give your empire benefits from holding those planets.
If you depopulate worlds in this way, you’ll have a lot of empty building slots and not many pops to work them outside of your core... so you can spam resource silos, fortresses (if you have the tradition that gives them +3 unity) or other buildings that don’t require jobs to work in order to give your empire benefits from holding those planets.