Just because an ability is awesome doesn't mean that you always want to use it. In fact, sometimes the consequences of using an ability are so severe that you need to think long and hard before you ever use them at all.
These are anime attacks that hurt the user. These abilities often bring the user significant benefit by diffusing dangerous situations when nothing else will do. But they come at a great personal cost. One example is Mankai from Yuki Yuna is a Hero, which gives the user a major power-up in exchange for a permanent disability. Another is Trafalgar Law's Op-Op Fruit in One Piece, which can grant another person immortality, but only at the expense of his own life.
Which of these techniques would you still want to use despite the high personal cost?
Naruto has so many techniques that harm their user that they could fill up a whole list by themselves. For now, let's focus on the Eight Inner Gates, a technique that Might Guy learned from his father and passed on to his protege, Rock Lee.
The Eight Inner Gates is a taijutsu technique that involves opening up the chakra pathways in a person's body. Normally, these are blocked because too much power being unleashed at once is potentially fatal. Removing the blocks is difficult and requires intense training, but results in a rush of power. Each time a gate is removed, the user is badly injured.
Anyone who uses the 8th gate - literally known as the Gate of Death - must sacrifice their life in exchange. This is how Guy's father, Duy, passes away.
Human Transmutation is a form of alchemy that supposedly brings people back to life. Not only is this virtually impossible to achieve at all, but the costs of trying are high. When Edward and Alphonse Elric attempt to revive their mother, Ed loses his arm and his leg, while Al loses his entire body and is forced to live with a soul that's fused to a suit of armor. When Izumi Curtis tries to revive her stillborn child, she loses some of her internal organs.
In the 2003 series, things get even worse - the process can also create homunculi who must ultimately be defeated. Both versions of the story are heavily themed around the consequences of human transmutation.
Dragon of the Darkness Flame is one of Hiei's most powerful techniques, but it's also one of his most damaging. He's able to summon black flames from the depths of the spirit realm, which gather around his hand in the form of a terrifying dragon. While he's able to eviscerate his opponents with it, the technique severely damages his arm and causes him agonizing pain. Eventually, he learns to control the ability more effectively, minimizing the damage it causes, but this is a long process.
Vegeta's attacks are extraordinarily powerful ones - and some of them are so powerful that even he cannot always withstand them. Final Explosion is a technique that obliterates the user instantly, which is why Vegeta only pulls it out when he realizes that defeating Buu is impossible otherwise.
It's a defining character moment for Vegeta because he never would have been willing to sacrifice himself for anybody else in the past - but it ultimately proves pointless, as Buu just revives himself afterward.