Window functions are great for any 'inter-row' calculations where you need to refer to values in adjacent or nearly adjacent rows based on the order you define. They are the easy way to calculate moving averages. They are usually the best way of paging through results in the order you define (e.g. getting row 30 to 40, row 40 to 50 etc.) cumulative totals as already mentioned, calculating rankings within sets of data, calculating relative contributions to a total. Sots of statistical stuff as well, but I know you're not into that, Steve!