People at agencies spend most of their day checking on work. Asana surveyed over 13,000 office workers and found that 60% of their day goes on chasing updates, looking for information and switching between apps2.
The agent makes a short list each morning with only the things a person needs to decide, and it handles the rest by itself.
Each item on the list comes with the facts already gathered. For example, if a client asks for work that wasn't in the contract, the agent finds the contract, checks what was agreed and works out a price for the extra work, so all you have to do is decide. Without these facts, someone would still have to find the contract and do the maths, and the list wouldn't save anyone any time.
Agencies usually notice extra work weeks later when they send the invoice, and by then it is too late to charge for it. Because the agent spots it on the same day and puts a price on it, the agency can talk to the client and get paid for the work instead of losing the money.