DAx has the features, very advanced features (mentioned later) that a power user needs, and is highly customizable, but doesn't require software or hardware ownership. For those capabilities that are not currently there, the customer reporting team often finds a workable solution that we can present to our client.
For the more basic users and executives, the dashboard often meets their needs; else the report tab can help with quick access to metrics that have already been built by analysts.
Lastly, the level of complex analysis in the tool still impresses. You can analyze web events at the event level, visit level and visitor level. You can apply filters at the report level (for all three - event, visit and visitor) or metric level (again for all three levels). On top of that, they have a concept of scope and rules which, combined with the 3 levels, can really allow a power analyst to ask just about any question and get an answer.