Good Thing n.,adj. [very common; always pronounced as if capitalized.
   Orig. fr. the 1930 Sellar & Yeatman parody of British history "1066 And
   All That", but well-established among hackers in the U.S. as well.] 1.
   Self-evidently wonderful to anyone in a position to notice: "A language
   that manages dynamic memory automatically for you is a Good Thing." 2.
   Something that can't possibly have any ill side-effects and may save
   considerable grief later: "Removing the self-modifying code from that
   shared library would be a Good Thing." 3. When said of software tools or
   libraries, as in "YACC is a Good Thing", specifically connotes that the
   thing has drastically reduced a programmer's work load. Oppose {Bad
   Thing}.


Source: The Jargon File