Excel workbooks are one of the slowest data sources you can use with Power Query in Excel or Power BI. Reading small amounts of data from small workbooks is usually fast; reading large amounts of data from large workbooks can be very slow. But what about reading small amounts of data from large Excel workbooks? I did some tests and it turns out that performance can vary a lot depending on where your data is in the workbook and how that workbook is structured.
Read on for some interesting findings.