I for one always flush. i grow hydro and do 3 flushes in the grow. If you do not flush you always taste the difference always. Been doing this over 20 years and there is a huge difference. A good flush is used in nutriendt feed switches to ensure to roots and system are clear and give you a good clean baselin for your new feed schedule. At the end I like to flush the last 5-7 days with ph 5.5 water and a flushing agent. The buds will taste , smell and burn much better then non flushed. Non flushed is always harsher, will have different tastes and you get a pop and weird burn on non flushed buds. I wont say non flushed bud isnt good but anyone who does it side by side can not deny the difference. Some who are not really connoisseurs may not caring but those who really get into the true characteristics of the strains always prefer flushing. In hydro you can get a salt build up if using nutes which I have had happen when I tried skipping fresh flushing during the grow.