Found an interesting article in which one guy did some datamining on some popular exchanges and their volumes:
https://medium.com/@sylvainartplayribes/chasing-fake-volume-a-crypto-plague-ea1a3c1e0b5eApparently a few of these giants are falsifying their volumes. Maybe because a higher market cap would make people think it's a more trustworthy exchange? I don't know if it's really worth going through all of that effort.
Would this have a major effect on the prices? I know we used to see huge differences in prices in the past, but now you won't see much more than a few percent here and there between exchanges.
Of course that this is done to benefit the exchange. From now since Centralized Exchanges are popular you must trust any exchange provider that they give true statistics about their exchange. Since many people are looking at volumes before they decide which exchange they are going to use it makes perfect sense to try to give false data to increase the likelihood of new users joining and staying on the exchange.