As someone that speaks five languages (one of them being Catalan), I have to concede it's the less useful. And only get to use it when I travel back to Spain.

But that being said, I find that there's never a good reason not to learn a new language if you are in a situation where you're going to be exposed to it on a semi-regular basis. So if that's why you're considering learning Catalan, I would recommend you to go for it. Even though it's by far the least useful language I know, I still think it's been a rewarding investment.

Some reasons why I consider it was rewarding, in no particular order: - It sometimes helps me infer the meaning of a word I've never heard/read before. - I've read a some good books from Catalan authors. - I sometimes enjoy playing a game where I try to find words that share the same root in most of the latin languages I know but not in one of them (e.g.: for 'window', it's 'finestra' in italian and catalan, 'fenêtre' in french but 'ventana' in spanish !). This seems dumb, but it's actually my favorite reason for learning new languages.