If you buy one that has a VUDU code, and go on moviesanywhere.com you can now link your VUDU account, your Apple iTunes account and your Google Movies account, and whoever else, and the movie unlocks on all those other streaming services. So if you buy a BluRay movie, you can stream it on your favorite streaming service provider thanks to MovisAnywhere (run by the movie industry - the one rare good thing they did).
I buy movies only when its one I really want and there's either an iTunes code or a VUDU code.
It's good to note that moviesanywhere.com, Kanopy, and VUDU (now Fandango at Home) sell your data and use it for market research (in addition to other things, there's no telling what it will be used for after it's sold). That said, for those of us in California "Kanopy does not sell your information. Kanopy does not share your information with third parties for money or other valuable consideration."
I do the same. Minor correction - it's no longer Vudu, it's now called Fandango at home. You also have to watch out for expiry dates on the codes. US only.
Paramount and Lionsgate are the only studios which don't participate IIRC.
It's also worth looking into if your local library offers Kanopy services.