Dechlorators are not always required - I hope that most of the long-term hobbyists here understand that. I do have grave reservations about novices or even oldtimers who have not really tried to understand water chemistry in captive environments or what utilities do to process "drinking" (aka potable) water.
Tank water is almost by definition to a scientist polluted - the organic load, the microbial load, the mineral and metabolite loads are greater than in the comparable source FW. That is why we do water changes, right? But some of those same materials (specifically the organics and the microbes & infusoria) are exactly what the chlorine is put in the water supply to guard against. Enough is used to protect the water through the (imperfect) piping supply lines and some period in the pipes of your house. Your tank has many times the load of the tap water, so chlorine is going to fight those things in your tank and is in the process used up. The catch is that the worse your tank is, the safer tap water is to use without dechlorinator - because it has more organics and more bugs uinless it in OTS (when the highly acidic conditions reduce the bugs a bit). This is one of those awful paradoxes where the worse your care is, the more careless you can be. But what about those of us who are not overstocked, don't over feed, and do large scale partials regularly and religiously? We are at greater risk. Ditto for folks near the water utility versus those by pipe much farther from the source. And what about those periods where the utility has the break int the network for repairs, etc, or if surface water is used and it is a high rainfall period? In both and in other cases the utility boosts the chlorine levels. You may get away with changes at some scale of 10-50% with "normal" chlorine, but if it is up 3x and you do not know this, the usual change level can exceed the normal chlorine-burnout use and the residue can harm your fish or filter or both plus other problems. Dechlorinators or dechloraminators are cheap insurance IMHO.