Watering with pure water at two gallons of water per one gallon of soil to eleviate either salt build up in your soil or to flush out an overabundance of nutes. Keeping a healthy environment for your plants basically.
It's a waste of time in soil that stresses your plants, and causes them to eat their own leaves instead of plumping bud in the last 2 weeks and stresses the plants. Just my 2 cents. Flushing is more a hydro thing.