The phrase "big difference" means that there is a significant or noticeable distinction between two things. It implies that the contrast or variation is quite significant. Full definition
What I'm encouraging you to do is make small changes to your day that can make big differences in how your skin looks and your overall well - being. (mindbodygreen.com)
Depending on how big the difference between your caloric intake and your total daily energy expenditure, walking 10,000 steps might not be enough to trigger any decrease in your fat tissue. (fitnessandpower.com)
However, the design differences underneath the bumper cover can make big differences in how much it costs to repair the vehicles after impacts at low speeds. (iihs.org)