From my experience Dirk, the users genuinely dont know what they want.

Giving them power pivot allows them to play with the data until they get what they want. We can then build what they want.

What tends to happen now is that they'll ask for everything.

We'll then have to say no and ask them what they actually need.

They'll have a guess (it will be wrong), we'll build what they ask for and then have to go through several itterations of that.

Frustrating for both parties.