Hi,
I am not sure what you are trying express in thread where your system have multiple options and based on business you can chose best in the system for your business process.
You can have contract and also scheduling agreement for a material but in case of contract you may need to create PR* from contract and then PO for that PR* where each time you need to create a PO but in case of scheduling agreement no need to create PO and based on scheduling term - you can receive material. With scheduling agreement -you can save time and resource too.
In contract you have various types of contract - quantity contract, value contract and central agreed contract, you can chose any one of them for your business requirement. May be in some case- contract created for plant only.
Not sure why SA will be creating from contract again.
Regards,
Biju K