Good TDD, well real TDD, provides the team with a heartbeat.
Everyone has a heartbeat, you know what it's like: continuous and clear, smoothly flowing, subtle yet ever so present and soothing. Its unlikely that you're explicitly listening to it, but you are without doubt subconciously aware of the supreme comfort and reassurance that heartbeat provides you each and every minute of your day. It keeps you alive!
Same is true with software development. And while Iterations, Stand-ups, and CIT no doubt provide an essential macro-heartbeat, those things aren't what give us that minute to minute assurance analogous to our human heartbeat. That's where TDD comes in - true TDD provides us that comforting development heartbeat to actually get us productively and happily through the day.
It provides the transition from story card to failing storytest (acceptance test). Then from failing storytest to the first failing microtest (unit test). Then minutes later to the first passing microtest. Then minutes later to the next failing microtest, then the next passing microtest, and our first refactoring. Then minutes later to our next quick cycle of "red/green/refactor". Then within an hour our first check-in. Then a few more "red/green/refactor" cycles and another checkin. And before you know it, after one of those cycles, boom, a passing storytest! A high-five and a final checkin, then home by 6 to see the kids.
Do you hear it? Thum-THUMP, Thum-THUMP, Thum-THUMP...RedBar-GREENBAR, RedBar-GREENBAR, RedBar-GREENBAR...
A development heartbeat.
It's this rhythm that guides you, that keeps you on track. Its what gives you the constant feedback to know, at every step of the way, that you're growing the right design, that you're satisfying the customer's needs, and that you haven't broken any windows. It's what allows you to move freely and move fast. It's this rhythm that makes you feel good. It's this rhythm that makes you feel alive and happy.
Ask anyone whose felt it. Once you've actually truly experienced this rhythm - this heartbeat - I assure you, just as with your human heartbeat, you'll find it unbearable to ever live without.