Templating is a pretty powerful approach to provide extensibility to a project/component/library. It can be used to deliver different behaviors and/or look and feel to different customers, or provide extendable open-source libraries.
There are a lot of template libraries out there that can be used in your project.
The problem with these libraries is that in most cases they provide you an ability to define "static" content (basically, HTML and CSS). And if you want to include some actionable content (e.g. handle events from outside the template, etc.) - it might be either tricky or impossible.
This session showcases how you can implement fully functioning React Component templates for SharePoint Framework web parts using SPFx Library Components.