What would be the benefit of having different deposit addresses, besides the privacy aspect?
1) So you can reliably tell the source of funds. If I make lots of deposits from Bittrex and lots of deposits from Bitfinex, if they each deposit into a different address, it's easy to track the source of funds.2) To help resist $5 wrench attacks. If someone can figure out one of my transfers to Poloniex, they can figure out all of them. That can let them know when I have cash and when I have cryptos and how much. That can be leveraged into them knowing when to kidnap me and make it hard for me to convince them that I have fewer bitcoins than I actually have.
Also, you can't so easily dismiss privacy. Privacy isn't just about personal dignity, it's also often a matter of necessity. There's a reason businesses don't tell every employee how much every other employee gets paid. There's a reason your competitors don't tell you how much they pay from distributors you also do business with. This is especially true with cryptos where people might read things into other people's actions and act on the basis of them.
