Unlike WhatsApp, Telegram works in the cloud, and, in addition, securely encrypts all traffic (including transmitted files). Thanks to this, you can use Telegrams on any device and share an unlimited number of photos, videos and other files (doc, zip, mp3, etc.).
Also, thanks to the distributed infrastructure and powerful servers, Telegram is much safer and faster than any similar application (WhatsApp, Viber, etc.).
In other words, you can use Telegram not only on your mobile device, but also on your home computer, and even online, which Whatsapp cannot do.