BDD and TDD - What are they for?

[CreativeEmbassy]

I'd like someone to give me very basic reasons for why I need Behavior
Driven Development (BDD, see RSpec) and/or Test Driven Development
(TDD, See Test::Unit).

I'm a fairly competent programmer. I think I use what they call an
"iterative" style of programming; I don't rush out to build the entire
program at once. I do a very small framework, then attempt to run it
and see if it's giving me the result I expect. If it's not, then I
figure out what's going wrong, and attempt to solve it before going on
to the next small part.

It looks like TDD does exactly what I'm doing, but introduces far more
code to the equation. One of the biggest features of TDD is being able
to run a suite of tests to make sure new features don't break old
features. Yet I have an eye for this while developing; I either fix
the upcoming problem because I know it's going to happen, or I'm doing
it wrong in the first place. Sure, I occasionally miss, but who
doesn't? I find the issue as quickly as I can and resolve it in an
intelligent way.

BDD looks like a way to make it easy for non-programmers to do
programming, but not having people keep several functions in mind at
any one time. And it also does TDD? Am I close?

But everyone continually praises TDD and BDD, which leads me to
believe I'm missing something profound that could make me a better
programmer. So what's the big deal?

I'm reposting this to the Ruby mailing list, if I receive any really
good answers I'll post them here.