Spring Boot 4 modularity is one of the biggest practical improvements because it encourages every microservice to depend only on what it actually uses.

For example:

· Order Service: WebMVC + JPA + Kafka

· Notification Service: Kafka only

· Cache Service: Redis only

· Authentication Service: WebMVC + Security + JWT

Each service carries only the modules it needs, which improves startup time, reduces memory footprint, simplifies dependency management, and makes GraalVM native images and Kubernetes deployments more efficient.