I'm hoping to be able to provide better service to some Chinese customers I occasionally see at my night job (hardware store) who have difficulty describing what they're looking for in English. I can't be sure what variety they speak (and if they speak a regional dialect of Mandarin, I would still be up a creek), and anecdotally, I gather that some Chinese immigrants in the US do not speak Mandarin fluently.
From what I understand, one of the difficulties of studying non-Mandarin languages such as Yue, Wu, or Min Nan is the fact that speakers of those varieties, from having to read Mandarin in everyday life, simply read and write Mandarin while speaking their own dialect.
Is this the common experience among Chinese immigrants? If so, I think I could focus particularly on reading and writing, which I'm already better at than speaking and listening, and have more of a guarantee of communicating effectively.