The library files (.PBL) contain source code and executable code. When you save an object in the painter, it saves the source code and compiles the object to also update the executable code. This is why the 'Run Man' can run the application instantly.
The 'Full Rebuild' option recompiles every object in the Target or Workspace (depending on which one you chose). A full rebuild is only needed if major structural changes have been made to an object that is referred to by many other objects, an ancestor window for example.
The Project Deploy will create .EXE and .PBD files (.DLL for machine code). It is recommended that you do a full rebuild as part of the project deploy. When a .PBD is created, it just copies the existing executable code from the PBL to the PBD. It doesn't recompile any objects, that is why the Project has a Full or Incremental choice but not a choice of None.
The Incremental Rebuild only recompiles those objects that it determines had references to objects that changed since the last time they were compiled.