You might have thought that the five "minisodes" that debut on the Doctor Who Season 6 box set DVD/Blu-Ray would be little more than filler or deleted scenes from the rest of the season, but really? There's a case for most of "Night and The Doctor" to be an essential part of Steven Moffat's Who canon.
The Curious Origins of These Shorts
Of the five installments of "Night and The Doctor," the final one, "Up All Night" seems exceptionally out of place - Not only doesn't it feature the Doctor or take place inside the Tardis, but it is pretty much an offcut from "Closing Time." It doesn't feel like it belongs with the (much, much more enjoyable) other episodes at all, and that's possibly because it doesn't; as the Doctor Who Confidential on the last disc explains, the first two episodes of "Night and The Doctor" ("Bad Night" and "Good Night") were supposed to be part of a serial with "Space" and "Time," the two Comic Relief minisodes from the start of this year (and not Children in Need minisodes from 2010; sorry for that mistake, when I was writing about this year's CiN minisode). That makes a lot of sense, thematically, and the second duo of episodes, "First Night" and "Last Night," could have been created to replace them... But why include "Up All Night" at all, in that case? It ruins the structure of the earlier episodes and doesn't really fit in with the other four episodes in any sense. Very odd.
"Is This What You Do Every Night, Then?"
The idea that, while Amy and Rory sleep, the Doctor goes off and has extra adventures is a great one; it enriches the character, somehow, makes him more... I don't know, more secretive and therefore more interesting, perhaps? Just the idea of all the stories that have happened that we didn't even know about because we, too, were sleeping... There's something about the idea of the Doctor having such grand adventures without anyone knowing that makes him seem more mysterious, and more fun to imagine who other lives for. It's such a small, silly thing, but I love it so much.
Another Classic Moffat "What If?"
The idea that deja vu is a result of time being constantly in flux is one of those very Steven Moffat "I'll take something that everyone recognizes and make it scary and/or sci-fi" things, but it's a good one, especially when it's brought up to explain just what happened following the reboot of the universe and rewriting Amy's history at the end of Season 5. It was completely unexpected, and very welcome, to see Amy's contradictory histories being addressed, considering it was never brought up in Season 6 proper.
Doctor, You Old Romantic
What makes the idea of the Doctor having secret adventures when Amy and Rory are asleep even more wonderful? The additional reveal that he shares those adventures with River Song. Add to that the fact that the Doctor went back for River on her first night at Stormcage, the line "The parents are asleep" and the sight of River becoming River ("I'm River Song!" she even says, and Alex Kingston's delivery shows her getting used to the idea) that makes the "First Night"/"Last Night" pairing irresistible. And that's even before we get to the end...
The Beginning And The End, All At Once
The reveal at the end of "Last Night" places some interesting teasers/spoilers into play for what we've got waiting for us in the next season of the show, especially if it's Matt Smith's last year as Doctor. Because we see the eleventh Doctor at a very particular time in the show's mythology, it suggests that said event is going to happen sooner rather than later - which makes a lot of sense, considering - but, because it is hinted at within the "Night and the Doctor" arc that has earlier made it clear that time can be rewritten (A long-running theme of Moffat's, and the show in general), it's also something that might be entirely undone at the last moment.
There's a lot for Who fans to love about "Night and the Doctor," and almost as much for them to pick through in terms of what it could mean to the show's larger mythology and character arcs. More than that, the first four installments are a short but sweet example of the sense of wonder, scale and just plain fun that Moffat has brought to the show since taking over two years ago; I wouldn't go so far as to say that they make the S6 box set an essential purchase, but if you're on the fence, they're definitely good enough to convince you to buy it.