I’m using Django and I used to use Sublime Text without any plugins which meant (at the time) it couldn’t automatically show me the definition of a function or object from a library, forcing me to search around for its documentation.
Switching to PyCharm/IntelliJ meant I could now just Command-Click (Ctrl-Click for Linux & Windows I believe) and see the actual definition and logic of the underlying function without having to rely on the online documentation. This of course works recursively, so I can repeat this process again and again up until I eventually reach the core standard library which is in C and isn’t introspective (at this point I can rely on my knowledge or some trial and error to figure out its behavior).