Agents are usually split into different groups based on their expertise. This way, all agents do not have to deal with all kinds of customer queries, something that’s very counter-productive. Each agent can specialize in one field and can be assigned to any queries in that field. For example, the Billing group can take care of all purchase/refunds and the Tech support group can troubleshoot product issues.
Groups can also be based on the working hours of the agents. Or even location of the customers who need support. For example, a Silicon Valley company can have a group working during their own business hours (GMT timezone) and another group to serve customers in Central Europe (CET timezone).