Yes, limiting the FPS helps to lower the load on your GPU and thus the power consumption.
As long as the limiting action decreases the FPS, it lowers the work of your graphics card. It's as simple as "less work, less power". I.e. idling your OS takes your computer less power in acting/calculating parts like CPU and GPU -> less power drain overall.
Also, if you're interrested in limiting the power of your graphics card or GPU, you may search the web for "Undervolting". This is often done with high end graphics cards to reduce noise, power drain and other possible unwanted side effects like coil noise.