It isn't about securely sharing highly sensitive material, but enabling verifiable privacy of typical communications. For example (hypothetically) me discussing cancer with a family member, or financial information, or (in countries where there is government oversight) organizing protests.
If not using a secure end-to-end encryption method such as chat, what do you recommend?
Email providers such as ProtonMail provide the same but in the form of email. Telephone calls are not secure, and neither are text messages.
For the things I post on Telegram I don't care about crypto but rather about a good desktop client, features months ahead of Whatsapp, nice niche communities, bots (including the hn bot which is really nice to see all things that have been voted above a configurable threshold during the day.)
Now that I think of it a lot of what I use it for is as a RSS and twitter replacement: subscribing to channels and groups, occasionally posting harmless stuff.