Hi,
an activity area is important for the warehouse order, and the warehouse order creation rule determination.
Activity Area - Warehouse Structure - SAP Library
The most important sentences are:
"EWM generates warehouse orders for each activity area.
When EWM generates warehouse tasks, it considers the activity area and copies attributes from this activity area, such as the deconsolidation group."
And it is always important to know that you do not need activity areas. With the exception of physical inventory. But they are very helpful.
Brgds
Juergen