This is the idea that if you can move your house to a different legal jurisdiction you can pick which laws you live under and change your mind if the situation changes. Eventually governments will have to compete for citizens instead of just having captive subjects to abuse as they want. If you can move your house then the "vote with your feet" method is much easier on the voters.
A seastead might choose to locate inside an existing land based country or be part of a new ocean based system. But this is still a powerful advantage even before there is a real floating country. This dynamic geography the reason that seasteads should be a game changer.
Patri has more on dynamic geography.