Federalism is very desirable because it allows different parts of the country to make different decisions, and this helps to teach us about what works. And what doesn’t.
It also means Americans can “vote with their feet” by migrating across local borders and state borders.
This happens a lot, as illustrated by this map from the Census Bureau.
While this map is fascinating, it also can be deceiving because some counties have very few people and others have millions of people.
It appears that internal migration might be a wash for states such as California and New York, for instance, since parts of both states are both green and purple.