Well, for Naruto in the fanfiction with future - seeing ability, a big drawback could be that it might change his personality. He might become more cautious and less impulsive, which is a part of what makes him who he is. Also, the knowledge of the future could make him feel a sense of powerlessness if he couldn't change certain events. And the moral implications are there too. If he saw something bad happen to someone and could stop it, but at the cost of something else, what should he do?
The drawbacks could be significant. He may start to isolate himself because he knows things that others don't. This could lead to a breakdown in his relationships. And if the wrong people found out about his ability, they would surely try to use it for their own evil purposes. He would constantly have to be on guard against that. Another issue is that the future he sees might not be set in stone. If he made decisions based on what he saw, but then the future changed, it could lead to chaos.
A possible drawback is that it might require a great deal of concentration. Naruto is already dealing with a lot in combat, like using his various jutsu and strategizing. Adding blood control to the mix might overtax his mental resources, making him vulnerable to attacks. Also, if his enemies figure out his new ability, they could try to counter it by using techniques that disrupt blood - related manipulation, like creating strong chakra fields around their bodies to prevent him from accessing their blood.
One drawback could be that it might disrupt the balance of powers in the Naruto world. Naruto was already a powerful ninja, and adding Sans' powers could make him overpowered compared to others, which might make the story less interesting as there would be less of a challenge for him.
Well, the main drawback is the damage to his body. The Eight Gates technique is very taxing on the body. Naruto could end up with permanent damage if he uses it too often. Also, it might change his personality. The intense power of the Eight Gates might make him more aggressive, which could be a problem when dealing with his friends and allies. And from a strategic point of view, if he uses it too early in a fight, he could exhaust himself and be vulnerable to counter - attacks.
His body might not be fully adapted to the new bloodline right away. Just like when he first started using the Nine - Tails' chakra, there could be side effects. His chakra control could be thrown off, or he could experience physical pain when trying to use the new bloodline - related abilities until he fully masters it.
One potential drawback could be the moral implications. Controlling someone else's blood is a very invasive and potentially cruel ability. Naruto, who is known for his kind heart, might struggle with using such a power. Also, it might be difficult to control precisely, and he could accidentally harm allies if he's not careful.
One drawback could be the strain on his body. The Sharingan is a powerful dojutsu, and Naruto's body, which is used to his own chakra system, might not be able to handle it well at first. This could lead to fatigue and over - exertion during battles.
One potential drawback could be that Naruto might accidentally hurt his friends or allies while using his super - speed. If he's not fully in control, he could run into them or cause a gust of wind that knocks them over. Another issue could be that he might rely too much on his speed and neglect his other ninja skills, like his shadow clones or his ability to sense chakra.
One drawback could be that absorbing too many bloodlines might make it hard for him to control his new powers. He could lose his sense of self or go berserk. Another is that other ninja might see him as a threat and target him more often. This would put him in constant danger.
One drawback is privacy concerns. Since personal assistants collect a lot of data about you, there is a risk that this data could be misused or leaked. For example, your voice commands and the information you ask for could potentially be accessed by unauthorized parties.
Fanfiction can sometimes deviate a lot from the original story. It might be that the official creators or those in charge of the Harry Potter brand don't want the characters to be misrepresented in fan - made stories, so they restrict access to it for Harry or anyone in the context of that world. Another aspect is that some fanfiction may have a negative or unethical undertone, and to protect the integrity of the original story, access is prohibited.