As an example, I use Evernote on my laptop and phone. I never need something like this, though, because Evernote synchronizes my data across devices. Likewise, if I want a convenient link for a long, hard-to-remember url, why not just use a url shortener?

EDIT:

Ah, I think I see your point now. The hypothetical website doesn't have an associated mobile app. If I'm reading the site on my laptop and want to switch to my phone, I could scan the QR code rather than typing in the url.