It's less an issue of size and more of economics etc. Also the precedent it sets for Catalonia's independence movement and the issues that causes for Spain is

It's less an issue of size and more of economics etc. Also the precedent it sets for Catalonia's independence movement and the issues that causes for Spain is another pain point that has been brought up (edit: Though as I understand it, Spain's position is that as long as Scotland does it "legally", and not by secession, they're fine?).