Senzu beans were originally introduced in Dragon Ball as a superfood that could feed an empty stomach for days. Goku doesn’t even use their healing properties during the Red Ribbon Army arc and it isn’t until after the Demon King Piccolo arc where Senzu beans are retconned to have healing properties. From there, the fact they can feed a person for ten days is never mentioned and they’re treated solely as a physical cure-all.
As Senzu beans are grown by Karin specifically for the Dragon Team to use, very few villains in Dragon Ball actually get to chomp on one. Which poses something of a problem to Goku on more than one occasion. Goku loves a good fight, and he’s willing to heal Dragon Ball’s strongest villains if it means he’ll get what he wants. Or so most fans would think.
In reality, Goku isn’t as bloodthirsty as he’s made out to be. Even in text, Dragon Ball rationalizes Goku’s logic in giving his opponents a Senzu bean. Whether or not this is naive on Goku’s part is certainly up for discussion, but there’s more to Goku’s actions than his desire to fight stronger opponents. When Goku gives a villain in Dragon Ball a Senzu bean, it means something– and it always comes with more than a few consequences.
4 Piccolo
By the end of his introductory arc, Piccolo is nothing short of the closest thing Goku has to an arch-enemy in Dragon Ball. He is evil personified, has a personal vendetta against martial artists, and is responsible for the deaths of Goku’s best friend & father figure. Come the 23rd Tenkaichi Budokai, Goku has every reason to kill his reincarnation on the spot.
Instead, Goku relishes the opportunity to net himself his first tournament win. Not just that, training with God for three years has humbled Goku and made him more passive– to the point where he doesn’t even feel the need to kill his greatest foe. If anything, fighting Piccolo awakens something in Goku: a deeper passion for martial arts.
Goku’s fight against Piccolo is a bloody battle to the death, While Goku strives not to kill Piccolo so he can win the 23rd Tenkaichi Budokai fair & square, Majunior holds no reservations. All the same, Goku is able to hand Piccolo a decisive enough victory where giving him a Senzu bean doesn’t prompt an immediate rematch. Desiring more from his enemy turned rival, Goku hopes Piccolo will train to give him an even greater fight next time.
3 Vegeta
Even though Vegeta serves as a main character as early as the Namek arc, it’s important to remember that it takes the Elite Saiyan quite a long time to fully transition into a hero. Vegeta’s not even a genuinely good person during the Cell arc, treating Trunks with cruel disrespect while directly allowing Cell to absorb Android 18.
Vegeta is very much a villain throughout the entire Namek arc, but that’s what makes him compelling. His actions fly in the face of the main heroes. Where Gohan & Krillin stealth around Namek, and Goku tries to avoid killing, Vegeta indulges in violence while gleefully slaughtering the Frieza Force whenever the opportunity arises.
Vegeta’s second major roadblock on Namek after Zarbon comes in the fom of the Ginyu Force. Recoome alone proves too much for Vegeta, Krillin, and Gohan to handle– all three left for dead by the time Goku arrives. Recognizing that he needs Vegeta’s strength (and that he was working with Krillin & Gohan,) Goku tosses the Saiyan Prince a Senzu bean. Of course, Vegeta ends up betraying the gesture by leaving Goku to fight Ginyu alone.
2 Cell
Easily the most controversial thing Goku does in all of Dragon Ball, giving Cell a Senzu bean is one of his boldest moves. Without telling a single soul his plan, Goku plots out a scenario where Gohan’s able to kill Cell during the Cell Games. This does end up happening, but not before Goku realizes that he might not know his son as well as he thinks.
When Goku gives Cell a Senzu bean, not every character sees the same thing. Cell sees Goku proving true to his word– Gohan is stronger and will put up a better fight. Gohan sees Goku completely misreading the situation– how could Gohan possibly be stronger than his father? Gohan enters the fight with little to no confidence as Cell pummels the boy relentlessly.
Piccolo correctly calls Goku out for throwing Cell a Senzu bean without so much as discussing a game plan with Gohan, but Goku was right to do so. In giving Cell a Senzu bean, Goku saved Gohan’s life. Without the Senzu, Cell likely would have just killed Gohan right away in order to get back to fighting Goku. Gohan wasn’t even registering on his radar before the bean.
1 Moro
Goku has since done it yet again courtesy of Dragon Ball Super. Beating Moro into submission with the full power of Ultra Instinct, Goku decides to toss the wizard a Senzu bean on the terms that he leaves Earth without making a fuss. Moro naturally does fight back– even becoming stronger in the process– but Goku wasn’t wrong to give him a Senzu bean.
Goku’s goal here isn’t to kill Moro, but to allow the Galactic Patrol to arrest & execute him as intended. Still, simply letting Moro go while weakened isn’t a smart idea. Moro’s magical abilities aren’t sealed away and he’s stronger than ever. Goku giving Moro a Senzu bean proves right then and there what Moro’s intentions are.
If Moro doesn’t fight back and goes without making a peep, Goku will know that the Galactic Patrol can handle things. Since Moro immediately tries to kill Goku upon being healed, however, Moro’s true character is shown: with time, he absolutely would have broken out again and likely done even more damage.