It's probably just an internal address... It's normal for exchanges to move funds around between wallets, create change addresses, combine many unspent outputs into one to minimise fees, store BTC in a cold wallet, retrieve BTC from cold wallets,... It's probably not a customer's deposit address since it received ~1400 BTC in ~1600 tx's.
In reality, it doesn't matter why bitfinex chose to use this address, they'll probably have their reason (technical, emotional, practical, security, minimising fees,...), however i doubt you'll ever know the exact purpose of this address without asking bitfinex directly.