
Explanation:

Box 1: Hide
Optimize data by hiding fields and sorting visualization data
Box 2: Delete
The fastest way to optimize your Power BI report is to limit the number of columns to only the ones you need in your data model. Go through your tables in Power Query and determine what fields are being used. Delete these columns if they are not being used in any of your reports or calculations.
Reference:
https://tessellationtech.io/optimizing-power-bi-reports/