What can I do here that I cannot do with a group chat?

A group chat loses things. A note posted in a Viber group in Bhadra is unfindable by Mangsir, and useless to the students who join the group next year. Here every note has a permanent address, a subject, a class level and a contributor's name attached, and it is searchable by anyone forever.

The other difference is reach. Notes shared here are readable on the open web, so a student searching Google for the topic finds them — which a message in a closed group can never do.