But there are some other really cool features in there as well.
First off, there are saved sets. When you put together a transmog set, you can save it much as you would save an outfit in the character screen (I still use the Outfitter addon, but that's more out of habit than necessity.) I don't know how many outfits you can save, but I'd guess many.
This way, if you get a new piece of gear, you can just head to the transmog shop and select the outfit, which will know which pieces to transmog automatically to your saved looks. Let's say you like to rock a tier 6 look on your Druid. If you get new shoulders and a new helmet while questing, it's just one button press to get those things looking like you want them to.
Of course, being able to save multiple sets means you'll also be able to experiment with looks and put them together before you actually spend the gold to transmog your gear. For example, I've been putting together a Paladin tier-8 10-man lookalike set (it's more blues and whites than golds and whites) for my Frost Death Knight, allowing him to get a kind of "redeemed" look. But obviously I'm also going to keep his old scary-looking Death Knight transmog set if I get tired of that look. With these saved sets, you can easily swap between full transmog sets just by using the menu.
But maybe even more exciting than that is that you can now set a transmogrified appearance to be only for a specific spec. Let's say you play a Mage. You dabble in all three specs, but your "literally on fire" look that you've put together for your Fire spec really doesn't work for Arcane, much less Frost. With the new transmog system, you can just put together that burning look and before you hit the transmog button, click the little arrow next to it and select "current specialization (Fire.)" This way, when you switch into your Fire spec, you'll get all that burning look, but when you're in the other specs, you'll have something more sensible, like the best tier set, Time Lord's Regalia.
So you can set things up to swap out appearance every time you change specs this way. I've got my Rogue on the PTR wearing basically the darkest armor I could find in all slots along with some daggers that have a bit of a purple glow from the Lifestealing weapon enchant illusion, but if he swaps out of Subtlety and into Assassination, it's a full set of tier 17 Poisoner gear with daggers out of the 4.3 dungeons that look like a tentacle and a jawbone and have sickly yellow and green enchant illusions on them.
Basically, you can always be dressed for your role. Transmog: best gold sink ever?