I started using it when we wanted to plan a re-union with my ex-colleagues. We were trying to use a WhatsApp group which turned out as a pain in the neck. Our main issues on W'app group were:
1. Not everyone spoke up / told what place and time they preferred
2. Few spoke a LOT
3. It was difficult to get all suggestions organised (We were 16 of us trying to organise a meetup).
Someone found Calio and created an event with the top suggestions included, we all voted and actually ended up meeting. We use it regularly since.