I know that most people are rather sceptical about the idea of putting their documents on the www, but if you think about it, the www is far less likely to disappear than your hard disk and nowadays you can store a lot of data on sites such as Box or Dropbox for free.
Well, as I've already said, the www is not going to go phut or disappear - you may back up your files on an external disk or USB stick, but external disks cost money whereas these sites don't - well, if you keep the size of the files stored there to between 1 and 50GB (ADrive will let you store and share up to 50GB for free).
If you have a PC and laptop or files that are stored on more than one beast being able to update and sync files can be really useful. Ditto if you work together with other people and need to collaberate on the documents you are putting together. If A updates the document, B automatically sees the latest version without A having to email it to B.
I've just co-authored a book for Longman and whilst we were writing it I uploaded my materials to the Box. Everything was in one place, my co-author could see what I'd written and the editor could access the latest version of the manuscript as well as earlier versions.
I lost about three units and a couple of weeks' work when my hard disk died when I was writing another book, so it was reassuring to know that everything was stored on my PC and the www this time round.
I dare say someone could crack the passwords and get at those materials, but then I dare say someone could also hack my PC if they wanted to, but I don't think the data they'd find there would be worth the time or effort.