Hi Dinesh,
These exception messages are pre defined in SAP and meant to inform MRP Controller about the event happened during MRP run. It also help controller to take action on such procurement elements.
Even if you do not assign exception message ID to BOM status, system will still release these exception messages in case there is some issue during MRP run. Either to inform user to take action or just for information purpose. Controller can later consolidate such materials together and take appropriate action.
During MRP run system carries out multiple activities in background, example net requirement planning, Lot size calculation, BOM explosion, scheduling etc...In case of unusual event for MRP relevant material, system issues a exception message at the end of MRP run. It could be related to lot size calculation or scheduling or any other process.
Lets take a case of 07 - Finished date in past, this happens when system carries out as scheduling of procurement proposal (say planned order) and finds during backword scheduling that Start date is falling in past. Now based in setting in customizing, either you can allow system to create order with past date or you can inform system to create order on today's date.
This way you can have different parameters or setting to take action on such exception messages.
Regards,
Rohit