There is presently a lot of talk about the Scottish referendum in September to determine whether it shall become a nation independent from the rest of the UK. I believe the Union has a lot going for it; English-Scottish ties are legion in people's professional and social lives with a lot of intermarrying and cross-border migration, so in those respects two separate nations with concomitant border-control nonsense could only make things worse (though need not necessarily do so; of course). There is in fact nothing too distinctive that separates Scotland from the rest of the Union. It is North Britain, really, and England and Wales are South Britain.
Yet, there are advantages to an increasing number of nations in the world. Since there is only so much surface on Tellus, more nations means smaller nations. Small countries should tend to be more open, because relying on domestic production is more difficult. Also, migration to "competing" political jurisdictions should be easier the smaller is the "own" jurisdiction, encouraging good policies to be adopted.
I can think of a couple of secessions which were followed by neat developments: Hong Kong (though I believe it took a while to really prosper) and Taiwan became much richer than Red China. Finland grew healthily after its independence from then-revolutionary Russia. Other cases are perhaps not so clear, though the amputated countries may not have done much better either (Eritrea, the Republic of Ireland may be examples of secession being followed by relative non-prosperity, although I am not an expert on these countries, particularly not Eritrea).
The new states after the Soviet break-up have been a mixed bag, but I am not sure there is one among them that has fared much worse relative to its initial position. And others have done very well. I know much too little about Pakistan and Bangladesh to be able to judge those cases, but maybe there is a slight tendency for secessions to be followed by positive developments (but are there adverse consequences for the amputated countries which cancel out the good things?).
In the particular case of Scotland, competition with Westminster will likely intensify due to the presence of Diasporas, both south and north of the border, easing transitions for Britons voting with their feet. Technically, a more decentralized Britain could accomplish the same thing sans any secessions, and what has been known as "Devolution" (essentially more "home rule") has meant small steps in this direction. Devolution currently means, as far as I can understand, that Scotland presently gets money to spend from Westminster without having to worry about how to raise it (I think the Edinburgh Parliament can adjust (some?) Scottish tax rates up or down by three percentage points). This is of course an unfortunate arrangement, but again does not technically require secession to be solved.
I am ambivalent about the issue. As I say, the Union has a lot going for it and secession is by no means logically required in order to have some things that would benefit Britons (and indeed everyone) today. Yet, it is possible that secession would be a good way of bringing them about. More radical and real Devolution would be my preference, but if that is off the table I am not sure what to think.
(PS. "Independence" is in quotation marks in the title of this blog post because no Scot would really be independent whichever way the majority votes in September; they will still be forced to pay taxes and obey rules imposed by third-parties which no Scot might choose for himself. The only difference is that the third party would then be a different government.)