SRCDS for windows places networking on a seperate worker thread allowing another core to take the workload when the main server thread is using an entire core.
This means you might get a few extra client slots however: as networking moves to another core it could affect the performance of servers that end up sharing the same cores.
As a consequence, you may get higher slot servers but you wont be able to host one server per core as CPU variance will be less stable.
Threaded Mode