Ormond:
There are a couple of very good advantages:
1 - You could upload files and retrieve them from anywhere in the world. No need to carry anything with you.
2 - You could store files privately (to be retrieved by you only) and publicly (i.e: provide a link to anyone you want to retrieve or view a document you stored on DropBox).
A a very good example for the Public link: Rob Markoff recently wanted to share a PDF file with us here on the Grumble. The best and fastest way was to store it in his Public folder on DropBox and then post a link to it here.
All the above doesn't mean though one should forgo the usual backup and having a physical copy of his files.
It's good to have Internet (or as they call now, the Cloud) storage, but having your own copy on Flash drive or external hard drive is also imperative, just in case the Internet is down or DropBox goes belly up.