Use of MDL macro vs passing file & line...

[dhcp.50.CHRIS94561 at spamgourmet.com]

I'm curious if someone could enlighten me as to when one should use the
MDL macro when making a function call and when one should simply pass on
the file & line parameters. Example:

int functionA (param1, file, line)
        int param1;
	const char *file;
	int line;
{
    functionC(param1,file,line);
}

int functionB (param1, file, line)
        int param1;
	const char *file;
	int line;
{
    functionC(param1,MDL);
}

Which is correct here? A or B? And why?

Any clarity on this issue would be appreciated.

Chris