Segment elimination
The data models in Power BI Desktop (and Power Pivot for Excel) are stored in column segments of one million rows. For example, a 20 million row sales fact table will contain approximately 20 distinct segments. If the data required of report queries is spread across all 20 segments, then more resources (and a longer duration) will be required to access each segment and consolidate these results to resolve the query. However, if the segments are ordered by date or perhaps by a given dimension (for example, store ID) and a report query contains a filter that uses this order, such as fiscal year or store region, then only a subset of the segments will be queried.
As a simple example, assume a 20 million row fact table is ...
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