A lot of people say that purely because of stability in the tank itself, which is definitely true but also comes from a time when it was harder to keep marine tanks. I find less easier to manage though and not as imposing in your home - my 28 litre was a breeze to maintain (without fish). Time to make up replacement water and space to store it is next to nothing. In heat waves I could just draw the curtains, throw a wet towel over the tank and aim a fan at it. Less glass to clean, lower running costs, time spent etc. Now I have a 100 litre water tank in my bedroom!