My two cents: Plugins allow it to extend Joplin with new functionality. Look through Any suggestions on what plugins could be created? to get an idea what could be done with plugins - from adding a spell check to support musical scoring or better highlighting of conflicted notes.
As the latest releases have put quite some effort into making it possible to create plugins, and Laurent needed to find out how programmers would use such a system, there was much technical chatter. And probably quite a few programmers will use the plugin system and API to support their (programming-related) use cases.
I'd expect that in the next months, there will be some further discussions about the technical points ("Help me develop my plugin" etc.). Which will then gradually shift towards people announcing "Hey, I've built a cool plugin for XYZ, check it out!". At which point you can just download any plugin that interests you and see if it extends Joplin in a way that helps you.