Agents are both traditional 'Travel Agents' and 'Channels' of distribution. This reduces confusion and allows one to think of an 'agent' as a business partner who sells rooms at unique prices and/or allocations.
Other functions you can perform with Agents:
For example: You might choose to 'load' (increase) your default rates by 10% to a specific Agent, and only sell the agent 40% of a specific Room Type. When the Agent went to their special web address, they would see 10% higher prices and only 40% of the available rooms.