Writers would make it a personal challenge to show Chuck Taine as a valuable part of the Legion. Brian Michael Bendis went so far as to proclaim him as one of the more powerful members of the Legion's latest incarnation. Here's some of what makes him awesome.
The Silver Age
When he first appeared in Action Comics #276 by Jerry Siegel and Jim Mooney, he was a Legion applicant, beaten out by Supergirl and Brainiac 5. He later joined after demonstrating how valuable his powers were before flight rings were invented. Always good-natured, he could be counted on as a morale booster when needed.
His tale encouraged new applicants since he had to prove his worth to the Legion. Bouncing Boy gained his powers after accidentally drinking a scientist's elastic serum. He set out to join the Legion but was rejected. His perseverance gave hope to Legion hopefuls, no matter their powers.
His power enabled him to inflate his girthy form into a spherical shape. He had incredible elasticity, able to bounce with significant force and speed. How he would appear would vary based on the artist. Favorites among fans are a ball with only vestigial hands and feet.
The Bronze Age
Chuck would regularly lose his power in one mishap or another. He also develops a close relationship with Duo Damsel after helping her through feelings of uselessness in the Legion. This would build to their wedding on Mars and the two leaving the Legion. Each would return to help the Legion occasionally and rejoined the Legion for a brief time following Earthwar, the biggest Legion event until The Great Darkness Saga.
Then the two would become instructors at the Legion Academy. There they'd train the next generation of super-heroes. In this capacity, they proved vital to the future of the Legion, producing future Legionnaires Magnetic Kid and Tellus and helping new Legionnaires Dawnstar, White Witch, and Invisible Kid.
The Rebooted Legion
Chuck Taine had no superpowers in the first reboot of the Legion. Instead, he was responsible for repairing the headquarters whenever it was damaged. It quickly became a full-time job. He was a constant fixture in the comics, demonstrating a deft ability to calculate angles and ricochet when Proteans invaded the headquarters.
When the Legion disbanded, Chuck helped bring the team back together with the ovoid ship he dubbed "the Bouncing Boy." When the new headquarters, Legion World, was damaged, Chuck and the mechanical being Gear worked together to repair it. When Earth-247 collapsed, Chuck Taine was among the Legionnaires that escaped in the Teen Titans/Legion Special and was seen when they left to travel the multiverse.
Legion of Superheroes Animated Series
Bouncing Boy was among the core Legionnaires in the first season of the 2006-2008 animated series. Throughout the series, he was very relatable and funny. He encouraged new applicants with his story of trying out for the Legion four times before being accepted. At the end of the first season, Bouncing Boy is the surprise winner of the election for Legion leader. In the second season, he grew close to Triplicate Girl after one of her three bodies was killed.
Superboy's Legion
In Alan Davis and Mark Farmer's Elseworlds series Superboy's Legion, Kal-El is raised in the 31st century. He forms the Legion of Super-Heroes with Cosmic Boy and Saturn Girl. One of the recruits from the first tryouts is Bouncing Boy, who didn't expect to be accepted when his friends Karate Kid and Ferro Lad were rejected.
Even after a disastrous loss to the Fatal Five, Bouncing Boy goes with a group of Legionnaires to Colu to rescue Brainiac 5. When the ship is damaged and falls to Colu, Bouncing Boy uses his inflatable body to cushion the crash and save the Legionnaires trapped in the wreckage. During the final battle with Lex Luthor, he rescues Superboy from a bombardment of red solar radiation.
The Bendis Era
This is where Bouncing Boy really showed his potential. When interviewing with the Legion founders, Bouncing Boy revealed that his power made him invulnerable. He also had a doctorate in metaphysical gateway science. In Future State, he was shown defeating an entire armada of ships scavenging Colu.
In Conclusion
Bouncing Boy is not a useless hero. His tale proves that everyone has worth and everyone has valuable gifts. For decades, he's been the personification of the lesson of the Legion of Super-Heroes. No one is useless, and no one is instantly rejected for failing to meet nigh-unachievable standards. Just remember that the next time someone puts out a list of useless characters.