Functionality {#2} influences:

• Product design, usefulness, look, feel, architecture
• User demands and acceptability
• General product risks, market selection and user type
• Environmental friendliness and product validation
• Documentation, training, service and support
• Compatibility with other products and user environments
• Component and material selection
• Standards, Reliability, Regulatory requirements
• All testing scenarios
• Upgrades, bug correction
• Legal, regulatory and standards requirements
• Installation, training, serviceability
• Consumables, fuel and energy requirements
• End-of-Life requirements and procedures

For example, if a product does not provide appropriate functions for installation, calibration (as required) and bring-up testing, then the product acceptability may suffer.