I'll elaborate a bit if you don't mind.... my understanding is rinsing or flushing at the end of a hydro grow (not sure about soil) is supposed to help the plant use up any remaining stored nutrients. This is desirable since unused nutrients can adversely affect odor and flavor! And while water is very good, the rinsing agents are designed to bind with the nutrients and purge them (along with other undesirable things). So using a rinsing agent may be a very good idea. I'm honestly not sure if this helps - but i usually flush with a rinsing agent for about 3-5 days then the last 2-4 days i use plain water - depending on how long i flush.
And if you noted the idea that unused nutrients are undesirable, then you'll also understand the importance of keeping the nutrient level as low as possible (while giving the plant all of the nutrients it needs and desires) which is quite the balancing act!