For me, though, I like the idea of being able to tell a running program (e.g. via a button or signal) to re-read a config file to cause changes to occur. It is nice if the file is externally validated before it is reread.
I just want to add that this only validates the syntax of the configuration file. Something that is not a big concern when the config file is generated as another monk pointed out. It still leaves the application viable to choke on syntactically correct although nonsense/false config statements (for example: setting a path to a file on a device that is no longer attached (usb stick for example)) or typos in the settings.
"WHAT CAN THE HARVEST HOPE FOR IF NOT THE CARE OF THE REAPER MAN"
-- Terry Pratchett, "Reaper Man"