I can honestly say that I a majority of the SharePoint projects I have been on, there has been custom BI dashboard development involved. It usually revolves around some level of upper management making the requirement that wants to track something in a pretty interface other than use numerics for whatever reason.
Sponsoring Management: “So we want to build a dashboard!”
Adam: “Ok, so what are we tracking sir in this dashboard”
Sponsoring Management: “You know, stuff”
Adam: “Ah, stuff, of course! How are we displaying said stuff?”
Sponsoring Management: “I want my portal dashboard like driving a car. If I am low on gas, I want to read a gauge and say, hey, I am low on gas. You know easy to read.”
Adam: “Ok, so you want the WebPart to draw out gauges. No problem.”
I think Dilbert gets the point across nicely: