Dark Energy is greatly beneficial to demonic entities and makes them far more powerful than normal.
Dark Energy can also grant transformations in some case as it allowed the demon Towa to take on her race's Dark form, and allowed the Spice Boys to undergo the Makyan Gigantification transformation. A Demon God can use Dark Energy to take on the Giant Demon God form. Dark Energy can also power up evil beings, and when utilized by an evil entity who is not a member of the Demon Realm race, it can allow the user to transform into a King of Destruction.
This energy normally only exists within the Demon Realm and Makyo Star, however Towa and Demigra managed to develop Dark Energy that could exist outside of these spaces, and used it to try and corrupt multiple worlds.
Due to its demonic nature, Dark Energy has a dark or sinister feeling compared to normal ki which can be felt via Ki Sense as noted by several characters.
Video Game Appearances
In Dragon Ball Heroes: Ultimate Mission X, the form is featured heavily in its story mode as non-Demon Realm race villains use it to acquire the King of Destruction form continue fighting. Interestingly, Makyans like Garlic Jr. take on the King of Destruction form and continue fighting. Garlic Junior's also causes him to take on his Gigantification presumably due to his race's affinity for Dark Energy as it is found naturally on Makyo Star.
In Dragon Ball Xenoverse 2, it is implied that this energy corrupts and augments the Fruit of the Tree of Might turning it into a demonically enhanced strain that can grant consumes the power of Villainous Mode and even cause their bodies to swell with Dark Energy and with further modification can be used to cast a new type of spell on the consumer that grants the first stage Supervillain power-up after shaving off the recipient's life to unlock greater power. Due to his status as a Demon Clansmen, Dark Lord Slug is able to sense this pure dark energy as it surges through his body before he becomes Supervillain Lord Slug.
"Nrgh...! N-No. It's Hirudegarn... He stirs! The beast's lower half must be nearby! Wait-no! Hirudegarn... is responding to the dark energy pervading this place. His return will spell certain doom for this world! The evil energy must be dispelled. Will you aid me?"
— Tapion noting the Dark Energy is weakening the seal on Hirudegarn in Dragon Ball Xenoverse 2
In a parallel quest, the Dark Energy of the Supervillain form causes the upper half of Hirudegarn that is sealed within Tapion to stir and must be dispelled before Hirudegarn can break free indicating that demonic entities like Hirudegarn can be strengthened by simply being in the presence of the pure dark energy emitted by the Supervillain form or it somehow weakens the seal that keeps Hirudegarn's upper half contained.