I use cURL a ton too, for when I want to make a one-off request, examine the response, and then throw it away. Here are some reasons why I'd reach for a tool like this:
• I want the history of every request and response to be saved by default, so if I ever need to look back to one I know it's available
• I'm sending several similar requests and I want them to share a set of variables, or, I want something in the response of one request to be used as a parameter when sending another
• I want to set a URL parameter with a bunch of symbols in without worrying about quoting
• I have so many types of requests that I'd like to organise them in a tree
• The JSON returned in a response is absolutely massive and I'd like to expand/collapse subtrees instead of viewing the whole thing as unhighlighted text
• I want the history of every request and response to be saved by default, so if I ever need to look back to one I know it's available
• I'm sending several similar requests and I want them to share a set of variables, or, I want something in the response of one request to be used as a parameter when sending another
• I want to set a URL parameter with a bunch of symbols in without worrying about quoting
• I have so many types of requests that I'd like to organise them in a tree
• The JSON returned in a response is absolutely massive and I'd like to expand/collapse subtrees instead of viewing the whole thing as unhighlighted text