Throughout the Dragon Ball series, the Z-fighters (Goku, Gohan, Krillin, etc) all hide their power. They try to hide their strength from normal individuals and their victories are hidden only for Mr. Satan to claim them. If they show their power it may encourage a form of support from humans like in the Buu saga and there may be other impacts such as the reduction of criminal activities. If the Z-fighters reveal their power it can be extremely helpful for the Earth as a whole. Why do they hide their power and not show the world what they can do?
Well, there are several reasons for the same:
- For instance, displaying their powers would result in them getting a lot of attention from the media and people, which is something they particularly would want to avoid. We see Bulma mention this to Vegeta before the Martial Arts tournament in the Buu Saga.
- The planet as a whole has accepted Mr. Satan as their most powerful elite warrior of the planet, if not the Universe. The People already believe Mr. Satan's true power is comparable to that of the Z fighters if not beyond. Having support from the planet doesn't really make a difference. The only time it sort of mattered was when Goku used the Spirit Bomb against Kid Buu, which Mr. Satan helped power up indirectly.
- Human beings are more of a liability than support. The Z fighters have a sense of justice and care more about solving the problem and saving the lives of people rather than getting rewarded or acknowledged for the same. If a bunch of journalists and media begin to intervene or come watch the Z fighters fight, it is very likely they would get killed or the antagonist could use them as leverage against the Z fighters.
- As far as crime is concerned, the Z fighters clearly don't have the time to stop petty theft and crime all over the planet. That said, Krillin is a police officer and uses his strength to an advantage against criminals and he is acknowledged very highly by his colleagues. When Gohan was a student, he spent his time-fighting petty crime as Saiyaman. It is also implied that Videl probably helped him as Saiyagirl after the Buu Saga. Adding to this, even Mr. Satan is several times stronger than an average human and he doesn't get involved in this situation. Even Videl, Chi Chi, and several fighters whose powers are nowhere in comparison to the Z fighters, are still strong enough to beat up petty robbers if they choose to.
Hence in summary, the only true benefit which the Z-fighters could possibly gain by exposing their power is probably attention from the media, monetary gain and probably expose Mr.Satan. Even if they did reveal their power, it seems very unlikely that people would believe that they are stronger than Mr. Satan. Also, Mr. Satan could also be considered a part of the Z fighters in a way, considering the fact that he's Gohan's father in law. Also, he's somewhat repaying his debt to them in the form of financial assistance at times, or small other ways in which he can help. The Z-Fighters strength is too significant to deal with petty crime and that is the job of the law enforcement and even them revealing their power, wouldn't really make any difference.
In conclusion, apart from the monetary benefit and publicity, there is nothing else to be gained from displaying their power to the world.
If the Z fighters reveal their power it will result in needy people asking for favours and may impact their lives. Media will constantly be on their backs and they will also ruin the lives of Mr Satan. The Z fighters don't have time for hero figures or justice they fight to protect and others like Goku "to get stronger". If the Z fighters reveal their power it will have a serious impact on their daily lives, on the live of Mr Satan as a whole and time for training would get taken up by their new heroic roles or if they do not waste their time presenting themselves as a hero their reputation will be destroyed. Keeping to themselves and letting Mr Satan appear as the hero seems the best choice for them.