Well, in my use of Google Books, if a book is under copyright you can't access the whole thing anyway. However, if you just want to use a small piece of the information in the book, you can get the information, get your citation, and move on. You don't even have to leave the house. Nice.
And I don't see the difference between accessing a book from Stanford's library online or going to Stanford's library and using the book or getting the book via ILL, other than saving gas and time. You're using the same book.