Best answer
The big one is that Telegram has no 24 hour window. Once someone has started a chat with your bot, you can message them later without a template and without an exception.
That single difference changes what is possible:
- Sequences that run over weeks work normally, rather than dying when the window closes.
- A reminder three days before an event is a normal message.
- Re engagement is a message rather than a paid template.
Other differences worth knowing:
- Deep links. A link can carry a code into the first message, so you know which post or which campaign sent someone before they type anything.
- Groups and channels, which Instagram has no equivalent of.
- No character limits as tight as the DM surfaces.
What Telegram does not give you is the audience. Instagram is where the comment on the Reel happens. Telegram is where the people who already chose you can be reached reliably. That is why the pattern that works is not moving from one to the other, it is the handoff: meet people on Instagram, and invite the ones who want ongoing contact into Telegram with a deep link.
Setup is also considerably shorter than Meta's. There is no business verification and no template approval, which makes it the fastest channel to test an idea on.
The Connect Telegram article covers the deep link codes, which are the part worth building properly.