In-story, it was explained that this made the combined bots 10 times more powerful.
In most cases, one robot formed the head, arms, and torso, while a second formed the legs and abdomen in a manner reminiscent of Victory's Multiforce. In addition, most of the Autobots took the form of combining toys, which the show called Powerlinxing. The star acted as a magnifying glass, revealing a faction sigil at the bottom of the hole.
The series-wide gimmick was 'energon stars', little translucent plastic things that slotted into holes on the Transformers. They immediately head for Earth, and while the Autobots and Decepticons battle the Terrorcons, an old enemy lurks in the distance. Alpha Q plans to re-activate Unicron to recreate his own planet (Unicron can do that in Energon) and so sends out Terrorcons to find energy to power Unicron. Meanwhile, deep inside all that remains of Unicron, the planet-sized Transformer, sits Alpha Q, prince of an ancient planet that was eaten by Unicron in ages past. Although Megatron is supposedly dead and the Decepticons and Autobots are allies, an undercurrent of shakiness pervades the Autobot cities. The show begins with Cybertronians living on Earth with humans and on the lookout for more energy.
Although previous series had followed the integral plot of Autobots and Decepticons searching for energy, Energon was quite heavily obsessed with it.
The sequel to Transformers Armada and the second installment of the Unicron Trilogy and the second (and final) entry to be animated by Actas, Transformers Energon ( Transformers Superlink in Japan) was concerned with the search for energon, the source of both Cybertronian factions' power.