I have two 55g fancy goldfish tanks and they will really look bare without it. But no you don't have to have it. I tried a few different ways but the one I like best and helped keep the water quality the best (besides 50% WC
's weekly) was going with Eco complete substrate a piece of driftwood that was tall but narrow that I would put against the back of the tanks where the goldies couldn't get stuck then add java ferns and anubia's. I then got some special rubbery plant anchors from Aquarium Plants.com and put in a couple swords, crypts (which they leave these alone) and in the substrate I put some narrowleaf temple, ambulia, and dwarf sag which they can munch on when the fancy strikes them. I do have to replace nibbling plants but have a supply in another tank. The other second choice was a bare bottom tank with a nice piece of driftwood and a few silk plants siliconed on. That tank was easy to keep clean! And at least had a little decor to spice it up.