It’s a convenient way to store and sort lots of curl requests for later use, its best cases are when you’ve got libraries of APIs you interact with semi-regularly (but not in such a consistent way that you’d be better off just writing a script). The paid version exists primarily so that you can have such a collection synced between an entire team automatically…but I’ve never worked somewhere that would be worth the cost.

For one off requests, yeah there’s no point to something like that.

Its user interface is kinda meh but it's pretty good for documenting and demoing an API across a developer team. However, Postman owns the data and upsells you a cloud solution.

A set of curl scripts or a .http file (httpie) held in your project's git repository is IMO preferable, most editors allow you to run these directly from the editor.

Because GUIs are a thing that a lot of people find useful

It's great for introducing people to HTTP, I always refer inexperienced new-hires to use it since it has proven to very effective at getting them up to speed. In many ways you could say Postman offers a GUI to the protocol itself, making it something you can visually explore.

I see stuff like curl as a more advanced tool for people who already know what they are doing. In fact Postman even offers a curl "export" option that lets you see how to do whatever you have done in Postman, using curl instead. So arguably, it's also a good introduction to curl as well.

It's useful for documenting and testing large sets of APIs in a team-based environment, especially those that use a variety of authentication options.

Testing and scripting between requests and being able to share collections with colleagues.