Imagine a developer has created a website for you using Bootstrap. On one of the pages, there is an accordion widget - for example an FAQ section with questions that show & hide the answers when clicked.
One day, you would like to add an accordion to another page on your site. If this site was using Bootstrap's standard accordion plugin, you would need to copy and edit the complicated accordion HTML from the existing page (fig.1). Tricky, eh?
But wait! Your developer has created the widget as a web component, so all you need to do is copy a few easy-to-understand, easily-updateable lines of code (fig.2) and fill in the blanks!
The benefits of this are: you don't need to re-hire a developer to make the change, or risk breaking your site's layout when trying to negotiate tricky code.