Good discussion here.
Lets look at why this approach works for anonymity, privacy and security.
(1) In terms of the network effect, your ISP (or anyone else watching the connection) won't know that you are mining Zcash, as they will just see Tor traffic instead. Arguably, network encryption can only buy you time, whereas anonymous routing can provide more certain anonymity. A combination of both is better still ofc.
(2) The pool operator does not know your real IP address if you use Tor, which could be used to determine your identity. They would still know your payment address, although user registration details can also be 'obfuscated' (by the pool operator and/or by the pool user).
Again, with the ability to make private Zcash transactions on the blockchain, the easiest attack vector for identification becomes the point-of-entry to the network (in terms of your own Zcash acquisition).
Given that users are likely to obtain coins in any one of three ways; by receiving a transaction!, by buying coins from an exchange or by mining them - further obfuscating some aspects of the modes of acquisition will certainly help towards the anonymity, privacy and security of the entire system moving forward.