I am no longer a believer in flushing (3X pot volume of water) for flavor and smoothness, but I do see flushing as a legitimate, albeit stressful, solution for removing excess salt from the root zone. I agree that plants do not consume salt, but in high doses in the root zone I believe too much salt sets off a reverse osmosis reaction that pulls moisture out of the plant, effectively killing it. If I am wrong on this, a correction would be appreciated. I have assumed this is why many of the synthetic nute labels recommend a flushing, because maybe they know they are recommending nute levels that are pretty crazy high.
The one time I personally experienced this is when I moved to a new house that had all of it water going through a salt based water softener, combined with use of synthetic nutes. My pots did not reach critical levels of salt content until late in flowering so it was a painful lesson.
So for me, flushing would be a last resort option for someone trying to finish a plant that had been overfed or wound up in fouled soil.
If you define flushing as going water only the last couple weeks, I think it is a more nuanced situation where people who have overfed will probably benefit and those with well managed plants will not.