Scented candles aren't typically used to create ambiance in a car because you need to light them for it to work. However, that might not be necessary in hotter climates during the summer.
Photo by islandjoe
As reddit user churninbutter points out, some places get hot enough to melt just enough of the wax in a scented candle to release the smell. While this won't work during colder seasons, it provides a nice option when the summer heat starts making things smell grungy.