This is the one of the best explanations of why the idea of 'flushing nutrients' out of your plants is a misconception. Rep for you. Right, the nutrients are converted to plant starches and sugars. Flushing is a myth.
Actually the real reason is not because the transported nutrients like nitrogen and potassium are converted into starches and sugars.
There might be something about too much nitrogen in the end product but that would only occur in severe overfeeding.
Which only is common in newbie grows.
Nutrients are not stored the way many people think they are.
Some nutrients are mobile others aren't.
What happens is that the mobile nutrients (like NPK) are moved to the calyx(es) and used up almost immediately.
No nutrients are stored in the calyx(es) at all.
Whatever surplus there might be (which will be very low unless you overfeed) is stored in the roots and stems primarily but also somewhat in the leaves.
My point is that you cannot prove pre-harvest flushing is a myth by saying nutrients are converted into sugars and starches.
You can disprove pre-harvest flushing by appealing to how nutrients are stored and used though.
Any grower who does not severely overfeed will never have a surplus of nutrients in the calyx(es) and therefore will not have any harsh or bad tasting weed.
Of course this counts having a proper dry & cure but most veteran growers know how to do that anyway so it's not even a variable per se.
Shivaskunk is correct about the chlorophyll but that goes for every plant, no matter how many nutrients it has been fed.
Chlorophyll surplus and/or dissipation is corrected during a proper dry & cure.
I do cut my nutrient feeding back at the end of flower. I peak with high ppm in week 5-6 and draw back towards the end. This is mostly to conserve nutrients and because the plants dont need it. I cut N out almost completely in the last half of flower. This leaves my leafs looking pretty yellow by the end. Like i mentioned before though this is more because i hate wasting money. The only thing (aside from shitty grown or dried weed) that i have noticed affecting taste is abundance of nitrogen in late flowering and that can be mitigated by drying properly.
As for how herb burns well i smoke joints and one hitters so i dont pay much attention. I have had weed that i bought refuse to burn in a joint though.
An abundance of nitrogen would be the result of overfeeding.
Which isn't very common for veteran growers who know their numbers and setup.
How weed burns is down to the drying & curing process and whether it's done properly or not.
Usually behavior (like burning, crackling etc.) is due to an improper drying period.
While appearance (including taste and odour) is determined by curing.
There are cross over variables though.
Like the crackling of weed which can be due to high levels of chlorophyll which hasn't been removed during a proper cure.
And the odour of weed which can be affected by a too quick dry (hay-smell).