(idiomatic) It may work differently in your situation, or be different in your experience.
Those batteries last nine hours in my laptop, but your mileage may vary.
(idiomatic) To express a possible difference in taste, "this is just my opinion, your opinion may be different".
That red dress looks really good on you, but your mileage may vary, of course.
Origin of your-mileage-may-vary
- In the United States, the Environmental Protection Agency requires a set of standard emissions tests on all new vehicles which simulate city and highway driving. Part of the test measures estimated city and highway gas mileage estimates. Since no test can exactly simulate all driving habits and conditions, actual gas mileage of each vehicle will vary. As a result, when these estimated mileage claims from automobile manufacturers appear in advertisements, they are almost always accompanied with the standard disclaimer "your mileage may vary."