Here is how it looks:
This feature is useful on devices with small screens. Also, it is good from a privacy point of view if you are working in a place where exposing your contacts is a bad idea.
Tip: You can hide the contact list completely. Refer to the following article: How to hide contacts from the left side in Telegram Desktop.
Telegram Messenger is a cross-platform instant messaging application which exists for all major platforms. The client software is open source and servers are proprietary software. Telegram supports special encrypted and self-destructing messages. It supports sharing of photos, videos and documents (all file types are supported, including very large files!). Telegram is getting popular because it had a strong focus on privacy before other competitors like WhatsApp added encryption. Also, not having a requirement to only use the official client is an important feature that makes this messaging platform more open yet secure. Clients exist for all operating systems making it ubiquitous. Conversation history is quickly synchronized across all your devices. And last but not the least - Telegram works independently on each device, meaning it does not require your smartphone unlike WhatsApp. This makes it one of the most useful messaging apps which exists today.