I have been using CTrip / Trip.com for about 10 years now, and can echo what's been said above about their customer service. I used to fly domestically within China quite often, and booking via CTrip saved me having to deal directly with Chinese carriers (and what would have almost certainly been massive headaches) on multiple occasions.

It can be hit-or-miss being able to pull up a reservation made via CTrip on some Chinese airlines' websites, and honestly I stopped bothering to try, but I never had an issue upon arrival at the airport. For those who are conscious of fare class for miles earning, CTrip doesn't usually show that info when selecting a fare. On the couple occasions when that info mattered, I was able to chat/call them and have them tell me the fare class before I booked.

I also usually book through CTrip if I'm flying certain Asian LCCs. Having access to prompt and competent customer service is one benefit. For airlines like AirAsia or VietJet, CTrip sometimes offers a different set of change and cancellation terms than booking directly with the carrier. You do need to look carefully when selecting a fare on CTrip, however. If you aren't familiar with the interface (which varies depending on which version of the site or app you're using), it sometimes can be hard to distinguish between whether the flexibility is built into the ticket price - making the full cost refundable minus any cancellation fee - or if you're paying a non-refundable add-on for cancellation protection.