Booking an online taxi in China, can be challenging (even impossible) if you don't speak enough Chinese. Even if you can manage to fill in all the blanks online, the taxi driver will call you back, and, trust me, his English will be even worse than your Chinese! He will ask you where exactly you will be standing and what you look like. If you know enough Chinese, you should definitely go out of your comfort zone and try it!
But I am not there yet. In addition, I often stay in service apartments in Beijing, lacking concierge services, and it is really not my style to just walk out in the street and try my luck during rush hour when I have an important time to keep; or when I have more luggage than I care to carry around looking for a taxi.