To start with the last part, in my opinion it is important to apply calculations and business rules consistently across QlikView applications. Doing this manually takes a lot of time and is prone to errors. Besides that, it is just not a very fun task. Fortunately, a lot of this can be handled by setting up a multi tiered environment with one or more QVD layers (for more information on this, see Rob Wunderlich’s excellent “Understanding & Best Practices with QVD files” webinar and slides).
Sometimes however, you need to use calculations that cannot be (easily) pushed to a QVD layer, for example when calculating averages or using set analysis. How can you store those calculations in a central place so they can be reused?