These tools serve 3 purposes:

1. To make theory more closely match practice that already works. This gives teachers something to teach.

2. To make someone who doesn't know what he's doing appear as if he did. This gives consulting firms profitability.

3. To help organize the System Development Life Cycle (waterfall process) of very large projects. This gives someone who knows what they're doing a few more tools in their toolbox.

My take? If you've really found good use for tools like these, then your project is probably too big. Break it down into smaller pieces, build a prototype for each piece, get feedback, and refine. It's not how quickly you appear to get started; it's how soon you deliver something of value.