e.g. If you had stored a plumber number 10 years ago, you'll receive a notification telling that the plumber is on Telegram now. Of course likewise, if you start using Telegram today everyone who has your contact and uses Telegram will receive the notification; be prepared for some awkward conversations with people whom you have forgotten.
•Telegram's latency seems to be low when compared to WhatsApp(Although part of which could be optimised code, data center proximity should account more and if so how a supposed renegade group of techies with no revenue afford better data center facilities than their Billion$ competitors?).
•Their feature update notifications seems to create a sense of consumer focussed entity when compared to the competitors.
•The bot API has made the platform extensible than others (Messenger restricted several features of their API after Privacy fiasco).
That's all, I don't buy the argument of Telegram USP as security and marketing it for one seems to be disingenuous at best and malicious at worst IMO.