I'm an older fish keeper. When I started keeping fish many many years ago, my local water supply didn't add chlorine to the water. That may be where the idea that conditioners aren't needed.
As the population grew, it became necissary to add chlorine. I've always added conditioner even when chlorine wasn't added to the water because it still helps with the ammonia buildup.
I always use conditioner in my tanks even when I'm not adding tap water during a water change. (sometimes I use Distilled or Spring water) Besides, doesn't some conditioners help with the fish's slime coat and relieve stress in new or sick fish, such as Stress Coat conditioner? That's the kind I use.
I don't think the idea should be to DISREGARD EVERYTHING from oldschool fishkeeping knowledge.
I think *adapting* older ideas into a newer idea is closer to the evolution of knowledge. Granted yes, technology tends to outdate methods rapidly (i.e. email vs snail mail); but stuff like fish keeping should evolve ideas rather than do away with the old.
Some people here have to fill buckets with the tap outside the house (one that connects to lawn sprinklers and such) because their indoor tap is not good to drink/not good for fish. Now, USUALLY the outside tap water is pretty cold, too cold for your fish.
So you can fill up a bucket and leave it overnight inside. Not only will the chlorine evaporate out (NOTE: chloramine doesn't evaporate out as quickly, and even then it leaves ammonia behind) but you will raise it to room temperature.
Using a dechlorintaor is just faster and more convenient if you need to do an emergency water change, and you don't happen to have an aged source of water anywhere.
@Kitty_Whiskers: I suggest you cease using distilled water. It messes up water chemistry quite a bit and does not provide nutrients required for healthy fish
Chloramines are the concern today, yes, they don't evaporate.
I remember Byron on TFK told me he never used dechlor for years on end, because his tap water never had chlorine. One day, the city started adding chlorine to the water supply without warning. Huge fish die out. x__x
Technicaly in natural form chlorine is a deadly gas also chlorination water can kill plants too.
Plants (and humans and animals) require some amounts of chloride to survive, depending on the size/composition. I know most topsoils that you can buy in stores have around 10-15ppm of chlorides to promote healthy plant growth...which is way more than the concentration recommended for swimming pools.