HTML pages depend on browsers, stylesheets, images, and sometimes live services. That is fine for a website, but awkward for a record you need to keep. A PDF freezes the page into a document.
This is useful for receipts, booking confirmations, invoice templates, email exports, internal reports, and simple web pages that need to be attached to another workflow.
HTML to PDF works best with self-contained HTML where the important styles and content are included in the file.