Security system expansion adds cameras, doors or storage to a system already in service. The planning question is which component reaches its limit first, because power budget, uplink capacity, recorder throughput and licensing usually bind before the camera count does.
An expansion is a chance to fix the constraint that was missed the first time. Adding four cameras to a full switch usually reveals a power budget problem rather than a video one.
Check the existing headroom
Read switch power and port utilization, recorder throughput and disk growth, then compare them with the addition. A recorder that lists 32 channels may not process 32 streams at full resolution.
Keep the records current
Update the address schedule, camera list and as-built drawings as part of the work. An expanded system with stale records costs more to service than a new one.