Flushing the salts from the plants roots and soil mix every month seems beneficial in my experience, however that is if your using a salt based fert ie miracle grow, foxfarms ect , if your running a purely organic grow ie guano/molasses tea bone meal blood meal ect. and no salt based ferts used then flushing would only destroy the living ecosystem you have created in the soil which is counter productive for your plants.
Now when it comes to harvesting all types of soil grows benefit from a flush, gets rid of the nutes and salts in the soil so you can really taste the true flavor of the bud, it also helps with the way in which the bud burns. There are a couple ways you can do this strait ph adjusted water for the last two weeks, which will cause you to lose a little weight or the Mr. O`s emergency flush described hear how-too-emergency-flush-using-bubbler-t29346.html
with the emergency flush you can push nutes until the last few days and then flush resulting in little to no weight loss.