This is not a new idea tbh mate iv been having this argument with my dad for a few years now, there is scientific evidence to back it up as well but for me I always flush and I wouldn't dream of not flushing .I grow in coco and I no it can hold nutrients in the coco easily if slightly over fed and when running seeds and different strains its very hard to give every plant the perfect amount of nutrients. Now my dad on the other hand he grows in hydro dwc and uses a automated feeding system called adwino (not sure how to spell it) basically it is a e.c/ppm and ph meter that is constantly taking readings from his main nutrient brain and it records and adjust the e.c/ppm and ph according to the intake of the plant, there for never overfeeding and u can physically see it on a chart raise the e.c in peak flower and then the e.c drop off towards the end of flower according to the plants needs , so I understand that his plants may not need flushing as he is only giving them exactly what they need . But ... if u are growing in a medium where nutrients can be stored in medium I think it is a must . Also to say flushing doesn't work is like saying if u overfeeding nitrogen and leafs claw and go dark green then lowering the e.c/ppm will not lighten the leaf colour. Obviously its each to there own and u should do what works for u .