Generally speaking...

The closer to your home and community a government is, the more control you as a citizen exercize over it. If individual sovereignty is not on offer, sovereignty at the lowest possible level is the second best. The larger the polity, the more distant that the government is, and not least, the larger the tax base it has, despite non-compliance rates, so the more repressive resources it has. I am not sure what the magic numbers would be, but beyond a certain size, every country is really an empire, not a democracy or republic. This is also why confederations (and sometimes federations) are also better than centralized states.

Just because of that, a Scotland and an England are better than a UK. (Indeed, England herself may also be too large.) And sure it plays a role in my generalized support for all separatist movements. Québec and Scotland were powerful referendum defeats, but we're still rooting for Catalonia and New Caledonia to win theirs.