In MPLAB X, there are distinct build buttons and menu items to build (production build) a project and to debug (debug build) a project.
When performing a debug build, the IDE will also set the configuration bit to allow debugging of the project by a debug tool, such as the MPLAB ICD 4.
In MPLAB X IDE, memory is reserved for your debugger (if selected) only when you perform a debug build. See What Do I Need to Do When Compiling to Use a Debugger?
Another difference is the setting of a preprocessor macro called
__DEBUG, which is assigned 1 by the MPLAB X IDE when performing a
debug build. This macro is not defined for production builds. You can make code in your
source conditional on this macro using #ifdef directives, etc., (see
Preprocessor Directives); so your
program will behave differently when in a development cycle.