Why would it be a mistake.
I hope the YES side wins. Scotland should be allowed to make her own mistakes.
I don't know the details of how the UK works. But if it's something analogous to Mississippi(or any other state) opting to go it alone as a separate country, it's a terrible idea. I can understand such a move if the seceding unit is
1) the engine of an economy.
2) is not dependent on the rest of the country for the same fortunes.
3) the rest of the country is actually a drag on its fortunes.
There might be other factors in play that Bryan wa Endebess might be able to shed some light.