You can associate a demand class with each sales order. When you place sales order demand, the forecast consumption process consumes the forecast with the same demand class. If the forecast consumption process does not find a forecast, it consumes entries that have no demand class. If a sales order does not have an associated demand class, the forecast consumption process attempts to consume forecast entries associated with the organizational default demand class first, and then consume entries that have no demand class defined.
Certain sales orders should not consume the forecast, because they are not indicative of what orders you expect in the future. For example, suppose you manufacture soft drinks, and have 100 primary distributors to whom you sell. Your sales order demand is roughly even across those distributors. One of those distributors has a special promotion on your product, and places orders for ten times their normal amount. The large order by this one distributor does not mean that your other distributors will order less. Therefore, you might mark this particular order as abnormal.
To prevent a sales order from consuming forecasts, associate the sales order to a demand class that does not have a corresponding forecast and is not the same as the demand class for your organization. In this case, the forecast consumption process does not consume any forecast for the sales order.
Suggestion: You should define a demand class for abnormal demand and assign it to an order type that you can associate with sales orders you might mark as abnormal.
The following diagram depicts the forecast consumption process: