There was a time (many moons ago) when I used "Chemical Nutes". Way back when, before it was called "Jack's Classic", it was owned by a different company (Peters) and it was called "Peters All-Purpose, 20-20-20". This had to be 20 or more years ago, about the time I found the Internet. I found that people were reccomending flushing - for the same reasons they state today.
Well, I tried it once and it seemed a little traumatic. I did some research and came up with the simple concept of "Over Watering". The idea is pure simplicity - just water until you get 20-25% run-off. What this does is provide a "Perpetual Mini-flush". I tend to use Organics these days and have reduced the over watering down to about 15-20%. I firmly believe that the perpetual mini-flush idea is the only good reason why we are incouraged to get a substancial amount of run-off.
So, this is my point: if you're watering to the point of getting a good amount of run-off on a regular basis - there is no need for a big time flush - because the stuff you want to flush is already gone.