It also allows for viewers to find things that may have been thought to be lost to time. There have been versions of The Phantom of the Opera that many "phans" thought were lost forever. Someone, somewhere, happened to have the version and uploaded and then, suddenly, it wasn't lost.
Then, as Ebert mentions, there are loads of 'free' movies available on YouTube, though not always in one piece. You may have to watch the movie in 10-15 minute segments, but it's there. Ebert himself states that the list of videos he's seen (for 'free') includes No Country for Old Men, A.I., The Ring, and The Grudge (Chapter 2 of Ebert). Here is a video I found within 30 seconds of searching that includes the entirety of the 25th Anniversary of The Phantom of the Opera: