One of the very useful features in Application Designer is the ability to compile the PeopleCode for a project. You can select Tools -> Compile Project PeopleCode from the Application Designer menu to do so. This is particularly useful for larger projects or when you are validating a project that has just been imported into an environment for the first time. If, for example, someone forgot to include all of the needed PeopleCode for things to work (maybe forgetting to include a needed application package in the project definition), then compiling the project and finding out about the problem immediately is better than hearing about later when a runtime error happens.
I prefer to do the Compile Project PeopleCode as a first step, before running the project validation (in the App Designer menu, Tools -> Validate Project) because the project validation stops at the first error while the compile PeopleCode will try to compile everything in the project and report on what it found.
Some enhancements in this area that we’d love to see: