The single-server topology is suitable for small to medium, single-site enterprises. It facilitates administration by a single administrator, but does not preclude the creation of additional administrator accounts as required by your Administration plan.
However, this arrangement concentrates the burden of network traffic (agent polling, data transfer, update deployment, and so on) on a single server, and the LAN that hosts it. As your network grows, the impact on performance also increases.
See also:
Using Directory Manager to group managed products
Understanding administration models
Understanding Control Manager server distribution
Multiple-server topology