The text contrasts the server utilization and scaling capabilities of MongoDB and Couchbase, highlighting the limitations of MongoDB's "Master-Slave" architecture which leads to underutilized servers and increased complexity when scaling. In MongoDB, only the primary server in a replica set can handle writes, leaving secondary servers underused unless they are needed for failover, which complicates scaling due to the need for additional servers and configuration. Conversely, Couchbase allows for more efficient use of server resources by enabling both read and write operations across all servers in the cluster, facilitating easy scaling and high availability without sacrificing consistency. This design difference translates into significant cost and complexity implications, as efficient server use can drastically reduce operational costs, making Couchbase a compelling choice for applications requiring scalable and cost-effective database solutions.