I haven't touched Postman since they started pushing me to log in, but for me it was just an alternative to hitting GET endpoints with my web browser or piping curl to jq. If I'm looking through an API's docs and figuring out how it works, I often want to quickly test endpoints and see what they return. I could've written a script to do it, but Postman made that slightly easier by removing the need to write code or remember syntax.