In a standard Ceroc class, although they teach sequences of moves, most often the only relationship between one move and the next is which handhold you finished / start in. This means you usually end up with one move you can do, one you can do if you work on / change it a bit and one move that's rubbish. How much technique is taught varies wildly from teacher to teacher. Principles seem to be rarely taught. This tends to cause leaders to focus on the one or two moves that you like, "doing the move" and then inserting it into your freestyle when you get the correct starting handhold.
It's tempting to think the same thing is going on in a tango class when they teach a sequence. However in a tango lesson you'll (hopefully) be learning 4 things at once.
Sequences are a series of movements put together in a way that you can then practice all the above. Ideally it works by chaining moves with dynamics that naturally set-up each consecutive move. The exception is when you're being taught the principle of how to lead something other than what is naturally suggested by the movement.
Movements are the lego blocks. After you've learnt them, most likely using the sequence, you can use them to build other sequences - sometimes known as freestyling.
Technique usually requires a teacher to point out. Eg stepping under her shoulder in a sacada. They're often too subtle to get on your own, especially if you're concentrating on trying to learn new moves / sequences. Unfortunately they're very important. You can do moves without them, but you're putting a serious limit on how well / smoothly you can do the move. Thankfully techniques tend to apply to groups of movements eg all barridas rather than just a CW left foot to right foot barrida from a giro. It's notable that weekly Tango technique classes abound, whereas the weekly Ceroc technique classes are only held in unicorn glades, somewhere over the rainbow...
Principles. The things you ignore because they say them too often eg "keep collecting your feet", or the heart of a specific type of move eg displacement is the principle in a sacada. It's really easy to think "I'm learning a move" because frankly that's what it looks like they're teaching. What's also happening is that they're teaching you one or more principles and the move is just a way of physically expressing them. How well they convey the principle they're teaching varies a lot from teacher to teacher. Principles are what makes the whole thing really work. Some are more universal than others eg understand "collecting" or "flexion" and you can apply it to pretty much everything. Understand "displacement" and it's much more limited in scope.
There's an important difference between "knowing" a principle and understanding a principle. I know that I should collect my feet, but until I can actually do it most of the time, I don't really understand it. Once you understand the principles and techniques that make up the movements, then you really can start to dance one step at a time.
Take a barrida. You can learn it in the sequence, sidestep, giro, enrosque, barrida. And then practice it. Provided you understand the principles of "staying on your axis", "leading with your chest", "from cross system collect, lead a pivot and move your foot into position for the barrida as she pivots" etc and the techniques of "it's not a ronde!" etc then something different happens. Moves beget moves. Before, if you wanted to lead a barrida you needed to go through the whole sequence - good luck with musicality, let alone the other dancers getting out of your way. Now that you understand the technique and principles however, anytime you're in cross system and collect you have the option to barrida simply by leading a pivot. If it doesn't fit you can simply do something else, or pivot and don't barrida.
There are a number of benefits with this. Firstly by understanding principles you can see what options are available to you at any given point in the dance. Secondly - and this is the big thing - there's a heck of a lot less of them. Good luck learning every single tango move. Learning the tango principles however is doable - still takes time, but doable. Likewise as a lead you'll be dancing the principles over and over in the evening so you build up experience faster. It doesn't matter that you're leading 4 different types of sacadas, you're using the same principle in each so you learn 4 times faster than if you just concentrated on learning each sacada as a move.
Oh and you actually get to dance, which is always a good thing.
- Christopher O' Shea