What role do expansion cards play in a computer system?

Expansion cards play a crucial role in adding additional functionalities to a computer system. These cards can enhance the system's capabilities by incorporating new features that may not be available on the motherboard. For instance, a graphics card increases visual processing power, a sound card improves audio output, a network card can add or upgrade networking capabilities, and a storage controller can enable additional hard drives. By using expansion cards, a user can tailor their system to meet specific needs, whether that’s gaming, graphic design, audio production, or networking.

While processing power, power efficiency, and heat generation are significant factors in a computer's performance and design, expansion cards primarily focus on augmenting the core abilities of the system through specialized functions. Therefore, adding additional functionalities accurately captures the essence of what expansion cards are designed to do.