I think that depends on where you are. Maybe someone will correct me, but I was under the impression that here in the US you can "format-shift" a DVD or BD you legally own by ripping it to an unencrypted format so you can watch it on your tablet or what-have-you. Isn't that the legal leg iTunes stood on (before ITMS) for ripping CDs to listen to on your computer or iPod?
You can make backups... with the encryption intact. But breaking DRM is essentially always illegal for any purpose, thanks to the wonderful DMCA. And that's before getting into EULAs that more and more frequently deny you ownership over what you bought, only a "temporary, revocable, non-transferable license to play this format on licensed devices in specific circumstances" or similar.
There's also still a chunk of blurays that it just won't rip because they're too sophisticated, although shocking few releases seem to be releasing those. (Must be a lot more expensive to make them.) You also run the risk that if you're not careful about what you put in your drive, you can have the latest Bluray disk revoke your drive simply by it spinning up and doing the initial read before you even ask for anything, from what I gather. I'm not sure if this is a current risk, but it's always changing.
I've also found there's some confusion about what constitutes a 'track number'. DVD only has one, Bluray seems to have two. Most releases keep both in sync, but not all of them. The STTNG Blurays were a bit tricky to get the right shows off in the right order.