Something you hear a lot in Catalonia is that the central government in Madrid takes more in taxes than it invests back into Catalonia.
There is some research to back this up, the most recent being a 2005 BBVA study that estimated this to be approximately €1094 per capita.
"Aha!" says the hard working, financially responsible Catalan, eyes lighting up with Euro signs. "If only we were independent, we could use this money for something better than supporting lazy Andalucians. Eh?"
Not so fast. What this independent minded person doesn't realize is that redistribution also happens at the European Union level. Richer countries contribute more than poorer countries and see less money back. The theory is that this money will stem the tide of Polish plumbers taking away jobs in richer countries.
Now suppose that the Republic of Catalonia wanted to be part of the EU. Catalonia would be relatively well off (buh bye Andalucia and Extremadura!), with a GDP per capita about the same as the UK or Austria. (note for Pedants: the EU budget process uses GNI, which is similar to GDP but would be slightly higher in Catalonia due to the large Catalan banks that lend money across Spain)
How much more per capita does the UK and Austria pay into the EU budget than it receives back? Drum roll please... €937 and €1024 respectively.
So nothing has changed, except that Catalonia would be supporting lazy Greeks instead of lazy Andalucians.
Las balanzas fiscales de las comunidades autónomas con la Administración Pública Central, 1991-2005