What does the update location and update cites do?

I added some 25,0000 business listings and the mapping feature was an issue. I was able to do a small test and the update location fixed that very small test. I have since reuploaded the large number and pushed the update location and it seems to be hard at it? What is it doing and how long should it take? Same question for cities as well? It runs then stops then runs again but no error messages at all going to let it run all night but just wondering what it does?