What do you mean by deterministic signing?
It takes the random number generator out of the process for generating a signed transaction. Somehow (I do not know the details). It makes it safer, as the signatures can't leak any information (i.e. something to help calculate the private key...) when using weak RNG implementations, plus some other benefits I expect. Also, it's last on the changelog list for 0.93
Oh so instead of random it uses a rolling nonce
Idk, personally I think a bad write can make you reuse an increment and boom you're done. But what do I know.
If it adds a random number, it sounds very good.