In Humphrey Sheil book Chapter 1 redundancy explained but confused with one point made as below
The redundancy dimension is the multiple systems that work on the same job, such as load balancing among several web servers. Redundancy is increased through horizontal scaling and is also known as width.
Redundancy can increase performance, reliability, availability, extensibility, and scalability. It can decrease performance, manageability,
i can understand that Redundancy can increase performance, reliability, availability and scalability but how it can increase "Extensibility".