I got bit recently. I didn't ask for requirements and I didn't create a design document. Bad Chet.
It made for a difficult time getting that first cut done...and I missed a few very important items.
Talking with a friend today about it, and he kind of hammered the point home. Do the design document and you spend fewer cycles spinning your wheels. As an example he use a project we both worked on last summer. At first, he didn't do a design document and "struggled" for a couple of weeks. When it came time to do it again (it had been dropped from that first release), he started with the design document and it only took a week.
Forced him to think about how to do it, the possible roadblocks and the ability to raise those roadblocks to the appropriate people.
For whatever reason, I had never thought of the design document in terms of OBIEE. I don't know why, it just was. For OLTP type applications, I would always, at a minimum, create a Visio diagram. That would allow me to quickly and easily spot any problems. That world is much more intuitive to me, so I can visualize it easier. OBIEE, not as easy.
So here's my pledge to, no matter how much I loathe formal design documents, to go forth and create formal design documents. After all, this is development, just a different tool (and a layer of abstraction). No more ad-hoc development for me.