Summary: Currently the hierarchy sizes limit in a Sales Forecast is just 5000 data which is not enough for the large organization who used the Sales Forecast on selling products which has many different models, variants, and types, the data will be more than 5,000 records. 

What need to be changed: Either expand the Hierarchy Sizes in a Sales Forecast to much more than the current size limit or remove the hierarchy Size Limit on a Sales Forecast.