Well, long ago i used to set it in that way so, when it crashes it automatically drop a debug file for gdb for futher analysis, you don't need to run the map-server under gdb console (maybe your pc crashes and you was under gdb, the connection goes down and the whole server too, so, in this case, it's more useful set an auto debug file while you go to eat, or sleep or whtvr)
Useful links if you can't understand me
http://rathena.org/board/topic/73548-stackdump-gdbcoredump/
http://rathena.org/board/topic/63290-making-crash-dumps-with-cmake/