Think of it like moving house
Data migration can be likened to that of moving house. In parts of Europe and America, some homeowners would pick their entire house from its foundation, tow it behind a truck and setting it down in another spot.
While this might seems like the fastest and easiest way to move houses, there could be a higher possibility of damaged furniture during transportation. And unwanted items that should long be discarded, are brought along for the ride.
An alternative to that would be, moving your belongings in batches and only bring with you the most essential items; the “need-to-have’s”. This would ease the burden of also moving the “good-to-have’s” that may otherwise complicate the migration process.