Circuit breakers for resource-intensive operations

I am preparing for system design interviews and ran into circuit breakers on hellointerview's Networking Essentials section. After some research, I get them. I understand the examples mentioned below with the exception of the one in bold regarding resource-intensive operations.

I can't think of examples that are uniquely different and are not 1 of the other 4 as a database call could be resource-intensive and so could an external API etc. What am I missing?

Some example sites to apply circuit breakers:

• External API calls to third-party services
• Database connections and queries
• Service-to-service communication in microservices
• Resource-intensive operations that might time out
• Any network call that could fail or become slow