It is a terrible answer (the one that has been down rated and hidden, thank goodness). A lot of people still don't know because not so long ago that is how it was commonly done. That doesn't make it right.
Now don't all cringe at once, but when I was a kid back in the dark age, I had a gold fish named Bobby who lived for years in a half gallon bowl. We had some kind of mother of pearl gravel in the bottom. We fed him some kind of dried fish food. Once a week we netted him, put him in a dish of water, and cleaned his bowl and gravel with dishwashing detergent. We rinsed the bowl, filled it with fresh water and put him back in. No temperature matching. No nothing. We didn't have dechlorinator. We didn't know about dechlorinator. We obviously didn't know much and we certainly didn't know better. He came from the dime store which gives you an idea of what a different time it was. He grew to a point and then stopped. We believed that is was natural for a fish to grow to fit its bowl and no more. At least he could swim and turn around in his bowl, not that it makes it any better. Bobby lived though the Cuban Missle Crisis, the escalation of the Vietnam War, and died about the time of the Six Day War, to name a few of the significant events during his poor little life.
Knowing what I do now, I feel extremely guilty. At the time we really believed that we were giving him a good home. Ignorance may not be an excuse, but it sure is a reason. I also feel extremely good when someone comes here asking how to care for their goldfish and they get the right advice. I feel sad when I see an answer anywhere like the one referred to. It is perpetuating the ignorant way it was done back in the day.