1. To store JSON. There's a pattern where when your webserver calls into some third-party API, you store the raw API response in a JSONB column, and then process the response from there. This gives you an auditable paper trail if you need to debug issues coming from that 3rd-party API.
2. To store sum types. SQL not supporting sum types is arguably the biggest deficiency when modelling data in SQL databases. There are several workarounds - one of them being "just chuck it in a JSONB column and validate it in the application" - but none of the workarounds is particularly great.
1. To store JSON. There's a pattern where when your webserver calls into some third-party API, you store the raw API response in a JSONB column, and then process the response from there. This gives you an auditable paper trail if you need to debug issues coming from that 3rd-party API.
2. To store sum types. SQL not supporting sum types is arguably the biggest deficiency when modelling data in SQL databases. There are several workarounds - one of them being "just chuck it in a JSONB column and validate it in the application" - but none of the workarounds is particularly great.