When you save a change to a menu item in your brand’s primary links config set, you’ll see a number of places that highlight where the differences are between the sandbox workspace and live/production:

The counter will increase by 1 for each setting/property that has been changed. So, for example, if you update 5 values for a single menu item, the counter will read as 5. Additionally, if you want to see the specific changes outlined, you can click the “Review & Publish” button and you will see a JSON blob of the before and after for each array item: