If checked, Jenkins will run individual module builds as separate builds. On a project with a large number of modules, or on a project where modules take a long time to build, setting this option to true may speed up the whole build, as different modules can be built in parallel.

Otherwise, leave it unchecked and Jenkins will build this maven project like you'd normally do from command line.

When your build uses "aggregator-style" multi-module aware mojos, you'd have to leave this option unchecked so that the mojo will have access to all of your modules.

Historically, this has been the default mode of the native maven project up until Jenkins 1.133. So if your project was created before that, you might want to uncheck this.