It is by far the app that I use the most on my mobile. For a lot of my contacts, I do not have their phone numbers, email address or full name. I also believe I do not know anybody that do not have a WeChat account (from my landlord, the restaurant down my work to the legal contact of some of our contracts).
I will be leaving Asia soon, I am not sure what will replace this while settling in Europe. My phone could only use WeChat, I will not see big differences, save for emails. What other apps are so central for other markets? I merely use Whatsapp but it is far from having the same extend of functionalities nor such a complete experience.