Parking lots are kind of difficult to navigate using GPS systems, since most of their collector roadways are unnamed. Further, because navigation is dependent on the location accuracy of a wide range of hardware devices with varying levels of accuracy that are beyond the programmer's control, IMHO any kind of turn instruction that based strictly on a distance of less than a tenth of a mile (about 500 ft) is irrelevant and more likely to confuse the driver than provide any kind of productive information. More often than not, the driver really has to navigate the parking lot visually based on what he/she sees across the parking lot, whether it is a specific store that is the destination, or finding these collector roadways within the parking to exit.
In my (limited) experience with Waze, I've found that the only real asset to mapping parking lots is either when a parking lot's exit isn't obvious from all places in the parking lot, as seen in the parking lot here
, or if there is a very large parking lot with multiple exits to multiple different roads, Waze can guide you to the most optimal exit based on your route from the parking lot, as seen in the mall parking lot here
Beyond that, however, parking lot routes have very little use, as once you turn off the public road into a parking lot, you have to visually find your destination and just drive to it, since the entire parking lot, no matter how big, is typically defined as a single address, and the navigator will take you to the same spot no matter which store in that parking lot you might be looking for.