The second incubator as a hatcher is the way to go for staggered hatches. This way the remaining eggs with later hatch dates aren't subjected to the higher humidity, jostling, and mess that hatching involve.
If you are using a turner with staggered hatches then you have to turn it off or remove it during the hatch and thus the later eggs don't get turned for a couple of days. Its just way easier to move the eggs on day 18 into a hatcher unit.
I think the mess might be the main thing. If you never allow eggs to hatch in the first incubator it will stay clean virtually forever. All the cleanup work will be confined to the "hatcher" while it awaits its next batch of eggs.
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