When you despatch the orders you fix in time their use of capacity and when you de-allocate them you remove them from the capacity planning table.
 
Dispatching:
 
While doing the capacity planning for the order you dispatch the operation. Dispatching operations is the main function of capacity leveling. Operations are dispatched to the time when there is sufficient capacity for them to be executed. You can also dispatch sub-operations and work elements.

Depending on whether finite scheduling is to be carried out, operations can be dispatched based on unlimited available capacity or existing available capacity. Existing available capacity is calculated as the difference between the available capacity maintained in the capacity and the requirements already dispatched.
 
Deallocating operation:
 
By dragging and dropping an operation from the work center chart onto any line in the pool you can deallocate individual operations.
 
To deallocate one or more operations, proceed as follows:
 
- Select the desired operations. 

- Choose Functions - Deallocate.
 
The system deallocates the operations. That means that they are put back into the pool.
 
When you create a production/process order the system proposed a data/time at which the operation has to be carried out in the work center. The same can be check in CM01, CM25, CM29, etc.

The MRP controller based on the priority of the order/operation/work center capacity he can deallocate the operation to some other date or time. If the work center is free at date/time proposed by the system then he will dispatch the operation. The status of the operation will be updated as DSPT(dispatched).

Sample Issue:
 
Dispatching Operation for maintenance order - CM25(Capacity Leveling).   
 
When we do Dispatching Operation for maintenance order through CM25 (Capacity Leveling).  What are all the backend process do & what are the fields will change & in which table the changed datas get updated.  
 
Solution:
 
In IW32, Extras -> Order Documents -> Changes we can see where the dispatch dates are documented in table AFVV.

See also
Rough Cut Capacity Load In Standard SOP

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