I read reviews all the time about the Battery life, or the lack thereof on laptops, but what about the performance of the CPU and graphics, or even the WiFi when on battery? Is the expectation that the system will performance just as well when on DC or is the expectation that there needs to be a tradeoff between power and performance ?
In Windows you can set up different power consumption profiles using Control Panel->Power Options. The most important two are when you are plugged into a wall outlet and when you are running off of battery.
So there is no expectation. It uses the options you have set up.