The worst part of using web components is dealing with the Shadow DOM, and templating in general. However when web components are just used to add small bits of interactivity to prerendered markup, they become extremely connivent, portable across frameworks/languages, easy to style, don't require immediate hydration, and do not require a custom server-side rendering step.
Behavior Elements is a simple utility function which aids in the creation of the sort of web components whose primary job is to add small bits of simple interactivity to such prerendered markup. Behavior Elements is best used in websites that are server-driven/multi page, because there is no rendering cycle, diffing, dirty-checking, global hydration, etc. it's best that all/most application state / routing reside with the server.
Behavior Elements aims to strike the balance between being simple, familiar, and easy to work with, yet still providing small additions of functionality/magic that reduces friction in common