According to the linked announcement the data size is 5-10% smaller. So you are exchanging a small processing cost for smaller storage size. It will depend on y

According to the linked announcement the data size is 5-10% smaller. So you are exchanging a small processing cost for smaller storage size. It will depend on your application but in many cases smaller disk reads and writes as well as more efficient cache utilization will make storing as JSONB a better choice even if you never manipulate it in SQL. Although the difference is likely small.