Chris Webb reminds us that Power BI incremental refresh can lead to some fragmentation:
A lot of people are building large datasets in Power BI Premium nowadays, and if you’re building a large dataset you’re very likely to be using Power BI’s incremental refresh functionality with your fact tables or manually creating and refreshing partitions in them. If so, you should occasionally do a special kind of refresh to shrink the dictionaries on your fact tables.
Read on for a test of the most extreme scenario, though even less extreme versions can be bad.