The fact that Telegram provides an API enabling third-party clients (like this one) is the main thing that sets it apart from the other big mobile chat platforms (WhatsApp, Messenger, Signal) for me.

It's really nice to have access to a wide variety of client softwares, and the ability to build ones own (shameless plug - I built https://github.com/d99kris/nchat which is a simple TUI client).