By consuming the essence of the Z-Fighter, you gain several boons:
*Ability to use Ki, starting at a level matching that of Son Goku when he fought Raditz (including physical fitness) that can be naturally increased with training. Of course, like any skill, if you stop training for a significant duration, you will start to get weaker unless you have another power that can remedy this. You can also teach others how to use Ki.
*Gain all unique traits and abilities of ONE race from the Dragon Ball mythos, with an optional appearance change to match said race.
*If Namekian, you instinctively know how to make your own set of Dragon Balls, which start out as powerful as Earth's set at the series' start. This can be increased with self-study and spiritual meditation, but takes months at the very least to figure out. You can spawn Mutated Namekian offspring (who are innately 100% loyal to you)by spitting up eggs like King Piccolo. You have a measure of control over their appearance and abilities, but they will generally never be able to pass as human unless you have other powers that could potentially influence your appearance or DNA, and by extension theirs. Vomiting eggs drains a lot of energy, the amount of which varies depending on how powerful you want to make the resulting offspring, so overdoing it can kill you. You can also spawn regular Namekians if you so choose. All offspring made this way can be classified into either the Dragon Clan or Warrior Clan. The Dragon Clan have healing abilities and can learn to make Dragon Balls like you, whereas the Warrior Clan is a lot more gifted in raw combat ability. You can also permanently fuse with other Namekians (including your own offspring) to increase your power, but all parties involved have to be completely willing.
*If Majin, then like Buu, you can absorb other beings' skills and powers by engulfing them. But this can also warp your personality and appearance depending on the kind of person you've absorbed. You can potentially split into two or more separate Majins if there's a literal internal conflict within you. You can asexually reproduce, albeit yours is different because you can literally break off a piece of yourself and make it into a brand new Majin. You can achieve a Pure Majin' transformation that makes you look identical to Buu and grants you his techniques at the cost of gaining the same madness that engulfed your progenitor. You can learn to control this power and retain your sanity while in this form, but it'll take time and training.
*You can build and repair all unique technology seen in Dragon Ball such as capsules, hovercars, scouters, spaceships, etc...
*You are an expert in any ONE martial art shown in the series, knowing all its signature techniques. Only training and live combat experience can push you towards true mastery. Note that a lot of characters blatantly steal techniques from each other, so a technique you thought was universal might actually be unique to a school. For example, Ki-based Flight was originally discovered on Earth by Master Shen of the Crane School, but characters who didn't study under him copied it after seeing it in action like Goku. While you can learn the techniques of other schools, you'll have to figure out how they work on your own. A difficult but not impossible task.