Actually many growers need to flush their grow medium. Not because it makes the weed smoke better but because they overfeed their plants and dump a gazillion gallons of bloom boosters on them. The grow medium is so toxic that flushing is probably the only way to keep the plant alive until harvest. Even then they end up with KFC plants that all the uneducated growers think look awesome.
Take this for example. All the people following that canuck clown on youtube raving about his crappy grows of fried to a crisp plants.
Yes these plants should have had the medium flushed out due to extreme overfeeding by a crappy grower.
And now I bring you the canuck. Nice plants huh? And he flushes.