In releases prior to Release 9.0, you can create Forecast allocation rules to add missing coverage dimensions to final forecasts, but not change existing dimensions. Also, such rules must be created separately for each item.
In Release 9.0, Forecast allocation rules were extended to enable rules to both change existing dimensions and add missing coverage dimensions. They can also do so without the rules having to be created separately for each item so, for example, a single rule created for all items can set the warehouse to a single warehouse on final forecasts when forecasts generated by site or over all warehouses are copied. The rules will also override forecast allocations calculated from demand history which they couldn't do before.
This enables forecasts generated over multiple product dimensions and warehouses to be consolidated under different dimensions, or just have their dimensions changed, when they are copied to create final forecasts.