Placing floating plants in an aquarium is definitely recommended. Besides producing oxygen and absorbing waste products, they also provide a hiding place for the fish present in the aquarium.
Some examples of floating plants that do well in an aquarium are: raft fern (Salvinia natans) and waternut (Trapa natans). These are fast-growing plants that can proliferate. Fortunately, you can very easily break up these floating aquatic plants and remove the excess.