It is not mandatory to have a sump in a fish tank. However, if you add one, you will receive the following benefits from it. 1. Tank sumps are excellent for setting up filtration media. You can place biological, chemical, and mechanical media in it. 2. You can also place the heater, protein skimmers, other equipment in it and save them from hanging outside the fish tank. 3. It adds tank water volume and helps improve the tank environment. 4. It boosts water circulation and aeration.