Is (Mandarin) Chinese actually useful if you have no plans of going to China?
I'm just wondering what all of your opinions are about whether Chinese is actually useful if you have no plans of going to China.
Well, there are numerous large communities of Chinese people across the world (like the Chinatowns of New York, San Francisco, and many other cities), and you can probably gain access to Chinese literature, television, and movies without leaving your country. You can also use apps like HelloTalk or Tandem to find Chinese native speakers to talk to over text; the internet essentially rids the problem of distance from finding people to speak foreign languages with.
Whether or not a language is "useful" is really subjective, and it's ultimately only as useful as you make it. If you try to use it, it could very well be useful, but if you don't, it probably won't be useful.
you don't need to know Chinese to go to China.
Unless you intend to engage an English-speaking guide all the time and/or only visit the most touristy places, I really cannot agree. I encountered very few people who could speak English to any useful level outside of places expressly geared to cater for Western tourists (and most tourist attractions on the mainland cater for the internal market). Staff at hotels will probably know a bit of English in the biggest, top-level cities, but don't expect them to know a word in smaller, more provincial cities (a city of several million is small by Chinese standards); shops, restaurants, taxis, trains—likewise, not a word of English.
In Hong Kong, on the other hand, almost everyone speaks decent English, but this certainly ceases to be the case when one crosses the border.
If he went there for a business trip, this is probably the standard experience. The company he was going to visit would make most of the arrangements for his time in the country. As a tourist, barring hiring a guide, the reality is as garpike lays out. I think there's a legal requirement that hotels with a license to accommodate foreigners have an English-speaking staff person. Whether this person happens to actually be at the desk when you're going to check in is a different question. Taxis are a particular problem. Without your destination written down in Chinese, it can really be impossible.
I would say that ultimately depends on whether you are going to use the language or not. Travel there or not, if you will use and/or hear, then yes. If not, then no it won't be useful... though in this case, I think the latter is most likely. Other Duolingo members will disagree but I don't care and stand by this.