Arma 3: Debug Mode
Arma 3, since 2.02, has an additional debug mode that can be enabled with the -debug startup parameter. Enabling it causes the game engine to be more verbose with its logging, providing additional contextual information for some information, and logging information that it otherwise wouldn't.
When in debug mode, many errors will provide additional context around where the error occurred. This will happen for script, Stringtable.xml and Description.ext errors, as well as in other areas. For example in scripts, this is the full stack trace showing error origin:
18:01:30 Attempt to override final function - ace_captives_fnc_doapplyhandcuffs 18:01:30 ➥ Context:  L582 (A3\functions_f\initFunctions.sqf)  L609 (A3\functions_f\initFunctions.sqf)  L608 (A3\functions_f\initFunctions.sqf)  L603 (A3\functions_f\initFunctions.sqf)  L605 (A3\functions_f\initFunctions.sqf)  L5 (z\gf_scripts\addons\gf_scripts\functions\fn_postInit.sqf)  L3 (z\gf_scripts\addons\gf_scripts\functions\fn_logHandcuffs.sqf)  L4 (z\gf_scripts\addons\gf_scripts\functions\fn_logHandcuffs.sqf)  L13 (z\gf_scripts\addons\gf_scripts\functions\fn_logHandcuffs.sqf)
Debug mode also unlocks additional errors that are hidden during normal execution. An example of it, coming in 2.08, is a check on getVariable that logs if it is called on a null object. To see more, see Arma 3: Error Messages.
A3_DEBUG Preprocessor Macros
When Arma 3 is in debug mode, an additional preprocessor macro is set that can be used by developers to change functionality when this mode. For more details see PreProcessor_Commands#A3_DEBUG