Kristyna Hughes looks at column encodings:
Power BI encoding is a powerful optimizing option that is often overlooked because it’s not visible in neither the Power BI Desktop tool nor in Power BI Service. Natively, the VertiPaq engine in Power BI investigates all columns in the data model and determines how it can store that data most efficiently. To achieve maximum compression, the VertiPaq engine starts by encoding each column which determines the method of compression applied to that column. There are a couple types of encoding – value and hash.
Read on to learn the difference, as well as how to push your columns to use a specific type of encoding.