I just have joined Discord because, I joined a language class and needed some way to communicate to the classmates. And all other people are on whatsapp, and hence it became official channel of communication. A fellow classmate was kind enough to join discord to have discussions and give me updates.

Due to network effects, whatsapp still holds lion share. It is not a problem if it is optional tool that has to be used just for talking to friends. But, I am seeing it is being used for even communicating to school children by teachers and schools as almost official channel! In such cases, there does not exist much choice, at least in my country. People just refuse to use mail or call directly.