I can't speak to the BWRs... The PWRS do operate with rods all the way out, and we adjust boron every couple of hours (depending upon time in life) to adjust reactivity. The rods are manipulated in and out a few steps every month or so to minimize fretting (undue wear in a single spot on the rod coating), but this has minimal reactivity affect. Beginning of life, we borate, as burnable poisens loaded in the core burn up, but then we begin to dilute, to compensate for fuel burning up.
As for the reactivity balance... You're a little off. It's pretty easy, and takes relatively little steam/power to rotate a turbine to 1800 RPM. So, we spin it up, and then let a speed control circuitry take over to maintain turbine speed. What is actually balanced is the load in MW on the turbine. The more load, the more counter force is placed on the turbine, and the more steam it takes to keep pushing it at 1800 RPM. That's a little simple, but your balancing MW with reactor power in order to keep things going, and ideally, 100% power is matched to 100% turbine output, so you're neither wasting fuel, or not getting the most out of your turbine.
Bill