Are there any benefits to having a glass (no substrate) bottom?

A friend of mine was telling me that his boss has a 20 gal tank in hit office with 3 goldfish in it. He doesn't have anything on the bottom of the tank, it is just glass and there is a bubbler in it as well. I asked if he had any decorations or anything like that and he said only a few large marbles that apparently the goldfish play with.

Quote from Chirianti

A bare bottom fish tank has its own advantages over a substrate fish tank. There can be good flow in a bare bottom fish tank as opposed to the substrate one as more flow at the bottom would disturb the sand and the plants. The maintenance is also reduced in bare bottom tanks.

That makes sense. Maybe this is why he does it. It makes it easier to clean. I can't imagine it is very fulfilling or attractive for the fish. Though I am not entirely sure goldfish care about things like this like other types of fish.

Quote from AmyLil

Actually Goldfish, Bettas, and Minnows will do just fine in a bare-bottom tank. Also, each species requires certain requirements with the tank. So the water type and temperature needs has to be checked.

What about hides? It would seem like many of them require some sort of place where they can feel safe and secure and not just out in the open.

Quote from AmyLil

That's the major advantage of planted aquarium over bare bottom tanks. Because some fishes need hiding places to hide from bigger or more aggressive fishes in the aquarium.

I guess this is fine if you plan on keeping one type of non-aggressive fish then. If you have different species, it is not ideal. I know they do it in the pet stores a lot but this is to allow people to pick fish out and they are almost always in a tank with only the one species.