mhmm good growers don't waste food at stages of growth where they realize it is not needed
If you want to flush then do so but it is not needed under proper management. Nutrients are dirt cheap, i can afford the few cents/pence/pesos that come with leaving some in the medium.
I'm not saying its bad or dosent flush, at best, some nutrients that are water soluble and not tied to the mediums cation exchange out but there is no need and hence most will omit this stage in favour of just making sure there is no overfertilization at any stage.
If you get round to germinating a seedling in a zero nutrient medium you will see that it struggles like hell to even grow and thats only if it manages to germinate in the first place. With that there will be no other stage that a plant can tolerate zero nutrients and flushing them all out is not good for growth regardless of stage.
I can go out on a limb here and easily state with confidence about flushing but i'm not disagreeing with those that flush. Futher to this i would say that flushing may fix overfertilization to some extent but it wont fix the damage to your plant or the crap taste you get, those that overfertilize and expect a two week flush to magically make their bud amazingly tasty are misguided.
Why do you want to flush so bad would be my question back, you dont have to if you dont want to...?