If checked, Jenkins will only build any modules with changes from SCM and any modules which depend on those changed modules, using Maven's "-amd -pl group1:artifact1,group1:artifact2" command-line options. If the SCM reports no changes to any modules, however, all modules will be built. See http://docs.codehaus.org/display/MAVEN/Make+Like+Reactor+Mode for more information on the Maven behavior this utilizes.

This functionality requires Maven 2.1 or later, and will not have any impact if "Build modules in parallel" is selected.