The biggest "homerun" case for LiveView is all of the forms where you'd typically do server side rendering then add a bit of JavaScript for the few dynamic pieces you need. Think about what you might typically see in a Ruby on Rails app. Lots of Ruby generating the views, a bit of JavaScript for client-side whatever.
LiveView can be used for way more than that, but I think replacing "glue" JavaScript is the most slam-dunk case.