The classic migration weekend exists because of one assumption: that data can only move once. Drop that assumption and the freeze disappears.
Live Sync keeps your source platform and Shopify continuously aligned. Products, orders, customers and stock keep flowing while the new store is being built, so both shops describe the same reality at any moment.
The switch itself becomes boring. You change DNS, Shopify starts taking the traffic and orders that landed in the old platform seconds earlier are already present in Shopify. No freeze, no catch up script, no lost revenue.
Boring is the goal. A launch you can do on a Tuesday afternoon is a launch you can fix calmly if something needs attention.