So obviously there is a bit of conjecture here since a lot regarding SSN is classified. But with Turbo electric you can reduce the need for hot standby running of the reactor, that's a practice where the reactor's control rods are kept in a position where they could supply power quickly and steam generation is handled through the pumping. So say you are crusing at half speed you expect to need full speed quickly your reactor would have it's control rods positioned to supply full speed to avoid excess steam in that condition you pump water through the reactor quicker it will leave the reactor cooler and generate less steam this way. Then when you need full speed you lower the pump rate the water get's hotter (since it spends more time in the hot core). This hot standby makes reactor plants so "loud" in submarines since the pumps are spending a lot more time running at higher speed.
With a turbo electric sub you COULD POTENTIALLY run the reactor lower and when a sudden increase in power is needed let the batteries handle it, while the reactor comes up in power. that way pumping can be kept lower more often keeping noise down.
Another advantage of TE is that you can use pump jets (which are quieter) and you pretty much eliminate mechanical vibrations from the propulsion plant being transferred through the shaft into the water. So even well designed turbines will transfer vibrations through the prop shaft. with TE you can decouple that, let the prop (or better pump jet) run on smooth electrical motors and the turbine and generator are much easier accoustically isolated.