The "mother nature does not flush" argument is getting old…. you're not following mother natures plan unless you're growing 100% natural organic in the ground (bat shit, worm castings ect..)
Mother nature does not use man mad (synthetic or organic) nutes so this argument is bunk. The nutes that 95% of growers use cause salt buildup and nutes remain in the medium and ppm on run off can get crazy, do non flushers ever check their run off? If you're 3 weeks from finish and your run off is 2k ppm and up not flushing ain't going to help anything you need to get that down low I water just ph'd water every other watering (though I've found a couple strains that don't dig that method, fixing that next time i run them) doing so keeps my run off ppm low and I just water with ph'd water for the last 2 weeks, no flush just normal watering. If you're watering every time with fert (and don't have a way to check your PPM) I would at least water with ph'd water the last week or 2 and if your ppm is way up there like I mentioned before… I'd do a flush at 2 weeks (run multiple gallons, if you're in 5gal pots use 5gal water is a safe bet) than just water with ph'd water as needed.
Grojak, you missed the subject the OP and I were discussing. He was asking about pre-harvest flushing and you are arguing about routine maintenance salt build up flushing which is something completely different.
hth,
Annie