Migrating without redesigning the information architecture just moves the chaos to a more expensive platform. Design the target first.
Broken inheritance and individual user permissions don't migrate cleanly. Rationalize access before you move content.
A pilot migration with one business unit surfaces every issue while it's cheap to fix. Skipping it is the most expensive shortcut.
If governance isn't designed before migration, the new environment starts sprawling on day one.
Users revert to old habits without role-based enablement at each migration wave.