The Jargon File (version 4.4.7, 29 Dec 2003):

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.


The Free On-line Dictionary of Computing (30 December 2018):

Good Thing

    (From the 1930 Sellar and Yeatman parody "1066
   And All That") Often capitalised; always pronounced as if
   capitalised.

   1. Self-evidently wonderful to anyone in a position to notice:
   "The Trailblazer's 19.2 Kbaud PEP mode with on-the-fly
   Lempel-Ziv compression is a Good Thing for sites relaying
   netnews".

   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.

   Opposite: Bad Thing, compare big win.

   [Jargon File]

   (1995-05-07)