What are the eligible demands for planning calculation??

Hi Gurus!

I need to have a very fundamental understanding about which I am really confused. While the planning process does calculations for recommending planned orders for supplies it basically goes through a process to identify available supplies and demands to fulfill. Now the confusion is with regard to demands. If we have sales orders and forecasts both and we consume our forecasts from sales orders then my understanding has been to consider only forecast demand as the valid ones for supply calculation otherwise supplies can be duplicated. Only in case of the sales orders within demand time fence we should consider