Hard and smart training are key, but the pump tells you that you have the correct environment meaning you are well hydrated and have nutrients that you should. The pump just means that interstitial fluids are entering the muscle and that wastes are being taken out. The pump helps with recovery, at least in my experience that's how I went about it. I do train a little differently than most however, and even when going heavy I always strive for a good pump.
I agree. its how your body tells you something is changing.