A single, automated monorail network can be dynamically configured for multiple capacities. While typical operations may call for a 4-car system arriving at 2 minute intervals, for example, the same network can be switched to a 6-car system arriving at 75 second intervals during peak hours.
This flexibility allows monorail to operate as either light or heavy rail depending on need.
The train sets are indeed expandable but the real benefit of monorail lies with the small headway required in an automated system. Headways, the distance between separate trains, can be as short as 75 seconds, allowing a 2 or 4 train system to carry many more passengers per direction per hour.
The new Line 15 in Sao Paolo, Brazil is designed to carry 48,000 people per hour per direction.