Advanced Templating
There are logic that can be too complex to be put on template.
There are also cases where you keep repeating complex partials everywhere or you may need to use a third party module to do something specific in your template.
HTML+ allows you to create your own tags and attributes using javascript.
There, you can import third party modules, make expensive calculations and manipulation to then render the markup as you want it be be seen on the page.
With custom tags and attributes as well as powerful partials, what you can do is pretty much limitless.