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

Your mileage may vary
 cav.

    [from the standard disclaimer attached to EPA mileage ratings by American
    car manufacturers]

    1. A ritual warning often found in Unix freeware distributions. Translates
    roughly as ?Hey, I tried to write this portably, but who knows what'll
    happen on your system??

    2. More generally, a qualifier attached to advice. ?I find that sending
    flowers works well, but your mileage may vary.?


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

Your mileage may vary
YMMV

    (YMMV) The disclaimer American car manufacturers
   attached to EPA mileage ratings.  A humourous way of saying
   that the thing under discussion will not necessarily give you
   the same results as the author.  Often used to convey the
   hardware dependence of Unix freeware distributions.

   [Jargon File]

   (2012-02-16)