Ann,
All three of these methods that you have mentioned are popular workarounds; however, I will have to agree with experts Rupesh and Dharma that all of the functionalities that most businesses commonly request in this area are not fully satisfied by any of these solutions.
In the 'strat 40' method, a new sales order will not be confirmed if existing cap constrained supply elements have not yet been created. In many companies, such orders are a substantial portion of their business. For companies in highly competitive marketplaces, this method is unacceptable since they must confirm NEW sales orders 100% at order entry time.
In the 'ATP against Planning' workaround, in order to get a consistent ATP it requires that forecasting be done at levels that are consistent with capacity consumption. In many companies, they cannot forecast in this way, instead forecasting using sales criteria (e.g. regions or customer groupings which share common capacities) and they do not wish to forecast by capacity criteria. In addition, both of the above mentioned 'ATP against planning' solutions totally ignore any finished goods inventory that inevitably finds its way into the FGs warehouses.
I also have seen 2 of these 3 workaround solutions used successfully! But, the main reason clients end up using these workarounds is because they do not wish to spend the money, time, and effort to implement APO. APO gives you more comprehensive solutions for cap based sales order ATP, and definitely offers the possibility to eliminate the drawbacks of the 3 workarounds you mentioned.
Best Regards,
DB49