Explain dependencyManagement versus dependencies in a parent POM and why it matters.

dependencyManagement only declares versions and scope centrally; it doesn't put anything on any module's classpath, so children opt in by declaring the dependency without a version and inherit the managed one.

Plain dependencies in the parent are forced onto every child whether they need them or not, which pollutes classpaths and blurs each module's real dependencies. The senior practice is to manage almost everything in dependencyManagement so each module explicitly lists what it uses, reserving parent dependencies for genuinely universal things like test libraries; this keeps modules honest about their actual coupling and avoids accidental transitive reliance.