What is Vtiger CRM Stock Reservation?

Stock Reservation comes into play when a commitment for sales or purchase for a certain quantity of a product is made but not delivered. Hence you reserve the ordered quantity for a product (Reserved Quantity). By not letting them out for sales or purchases. Stock Reservation is required during various scenarios such as commitments or deals where in customers:

• Order products and want them delivered at a later time.
• Initially make partial and later complete payment after products are delivered.
• Initially require a partial and later complete quantity of products delivered.
• Despite the complete payment, are unable to receive or delay delivery of products due to business inconveniences.

Stock Reservation lets you unreserve or release the Reserved Quantity for products and add them back to their Qty. in Stock. Along with creating Sales Orders for the same during their delivery. It also lets you cancel and set an expiry date for the Reserved Quantity for products. 
Once a Stock Reservation record for a product is reserved or unreserved, canceled, expired, the Qty. in Stock value for a product in the Products module is auto decremented or incremented respectively as much as the Reserved Quantity for a product in the Stock Reservation module. With the Stock Reservation module you can:

• Create a Stock Reservation record
• Reserve Qty. in Stock for products
• Unreserve Qty. in Stock for products
• Cancel reserved Qty. in Stock for products
• Set an expiry date for the Reserved Quantity for products