Some thoughts on the what and why of the treatment might help. Things make more sense to me when I know why.
Too many think of chlorine as instant death while I think of it as more like the fish and plants getting a bit of sunburn from the chlorine. Each time they meet a bit of chlorine, the chlorine will react with the fish or plant. The reason for using the treatment is to prevent this. Over time, it can work like getting burned repeatedly and it can harm the fish, etc. It won't necessarily show right away but it may be burning the gills and sensitive spots. We never know what happened but it is possible for the damage to be there and the fish just doesn't grow or live as long as it might. Something like sunburns and skin cancer to me.
It gets down to what amount of trouble you want to go to in trying to keep your fish in good shape. I spend so much money time and effort on the hobby that slacking on using a water treatment seems wrong, even though I can't see the damage. How many really deep sunburns can we get before we see the true damage?