From Star Wars: Revenge of the Sith all the way to Star Wars: The Rise of Skywalker, Force lightning was Palpatine's go-to movie when it came to finishing his foes. Even if the lightning cost him his life twice throughout the franchise, it was still a flashy way to show off the power of the Dark Side. Throughout every movie and TV show, only the Sith have been seen using the ability; however, that doesn't necessarily mean it's exclusive to them.
What Is Force Lightning in Star Wars?
A canon reference book, titled Star Wars: The Secrets of the Sith, mentions the use of Force lightning. It's described as "attendant energies generated by the dark side," that can be "channelled into concentrated bursts of the electricity capable of incalculable devastation." Given that it's only use is for offense and to cause harm, the wielder cannot use the power unless channelling their inner darkness.
Used sparingly, a burst of lightning could kill and disfigure their target, often being a slow and painful process. The canon reference book goes on to say, "Even the greatest of Sith Lords are not immune to the destructive efforts of this dark display," which is shown when Rey deflects Palpatine's own lightening back at him.
As seen when Darth Sidious struck Mace Windu at the end of Revenge of the Sith, a defenseless target will be stunned and barely able to control their movements. The lightning is so powerful that even the victims skeleton can be seen, and very few know how to deflect it. Yoda is the only person seen to defend himself against Force lightning without a Lightsaber, as he captured Count Dooku's lightning in his hands and re-directed it back at him.
It also appears that Force lightning comes in many shapes and sizes. The smaller burst of energy is typically seen being used, as it's small enough to keep under control. However, at the end of The Rise of Skywalker, Palpatine is able to strike a burst of lightning so large, it fills the entire sky and beings down all electronics.
Force Lightning Isn't Only For Sith
Chronologically, Count Dooku is the first to use Force lightning in Star Wars: Attack of the Clones. He then goes on to use it extensively all throughout Star Wars: The Clone Wars, with he and Palpatine being the only people seen to use it in the prequels. From this, it could be safe to assume that the power is only available to the Sith. However, any trained user of the Force could use the ability, but it was just frowned upon by most.
During The Rise of Skywalker, Ray accidentally uses Force lightning on the planet Pasana, believing she accidentally killed Chewbacca. While this moment was used to hint at her Palpatine heritage, it also shows that anyone can use the lightning, but only if they channel their anger. Given its destructive nature, it's no surprise that the ability is frowned upon in the Jedi Order, as they're sworn to keep away from any feelings of anger.
Force lightning is undoubtedly a powerful, and morally questionable, move. Although it's probably for the best that the Jedi don't use it. Not only can it bring the wielder closer to the Dark Side, it's also too unpredictable to control. During Palpatine's fight against Mace Windu, and final confrontation with Rey, he locked himself into a lose-lose situation with his lightning. If he continued to zap them, his lightning would be reflected back until he died, yet if he stopped, he would be left vulnerable to their Lightsaber attacks.