alt Hacker NewsI find tremendous beauty in the idea that HTML is just a syntactically structured document and in a perfect world you can render it to paper, voice, braille reader, screen, e-ink, etc. I'm equally attracted to the idea of asking an HTTP API for your desired content-type.
But in practical terms it's often just a distraction. You should do it if it's worth doing. I can imagine some websites having almost zero audience for "I want this printed" while others probably have a considerable audience (though oftentimes they just point to a .pdf which offers better layout guarantees). Some websites should be printable.
Any kind of statement, confirmation, or receipt should be printable. Some places still require printed documentation of expenses for reimbursement (even if it's only to turn around and scan it; you can argue it's silly but that doesn't mean it doesn't happen). A paper print is also an easy, cheap, immutable and durable one-off backup for anything you're looking at on your screen.