Yes, payment systems.

Until recently WeChat Pay and AliPay could only be used with Chinese bank accounts in China, and to get a Chinese bank account you need to get a Chinese mobile number first.

If you are a frequent traveller and read Chinese, it isn't especially hard to get a mobile number and bank account other than preparing to waste half a day standing in lines. After that, life is heaven for you because you now have access to all the convenience of the myriad e-commerce websites and apps.

Any other visitors would have tough time getting train tickets, booking accommodations, renting bicycles, hell, even buying from vending machines or automated convenience stores, because people really don't use cash anymore, but the system is really only designed for domestic users without much thought for short-term visitors and tourists.

I've used Didi extensively as an American in China, among other apps, both in local dialects and in English. I don't speak any dialects but rely on coworkers and in region partners to be all "just push this button and enter what mall/hotel/restaurant you're going to." Works with my personal/corporate cards.