To list a few benefits:

- e2e encryption

- many extra chat features (reactions, stickers, replies, polls, etc). It might seem unnecessary but imo they do genuinely increase functionality and ease of communication

- scalable to large groups (maybe sms is as well, I've never tried more than 3-4 people)

- don't need a phone, can message from a computer instead

- messages sync across multiple devices

- video calling for groups with some apps