Sexual Relationships 
Sexual Health 
Manipulating which means controlling / Influencing your partner is one of the high risks stunts in relationships. off course manipulating can be done in many ways i.e. Positive or Negative but it can cost you end of your relationship.
There are many questions on G@G from women about their partners watching porn and they don't want it. They feel insecure about it and hence want to stop it i.e. manipulating his mind.
Manipulation in relationships is somehow expected as we've to adjust a bit to live with someone else. But there are many people who try manipulate their partner and from my experience, it makes things only worst.
There are several reasons for which you should not manipulate
Everyone loves themselves
As like you love yourself, your partner does love himself. That doesn't make him Narcissists. If you try to manipulate them, it will change their personality. Manipulation is like Inception (yup the movie) it'll affect the future and the way of seeing past. In my relationship experience, people love to be with you only because they can be themselves with you.
Controlling is Pure Dominance
It is simply written in the definition of itself. Manipulation = Control. There might be some people who like that type of dominance but the majority doesn't like it especially from their partner.
It threatens transparency in relationship
It might not sound related but it is. Suppose you're telling your boyfriend not to watch porn. After some arguments, he'll accept it. He'll promise you that he won't watch porn ever again. But everyone loves to watch it! He'll continue to watch it but behind your back without letting you know it. Even if you ask him, he'll lie to you and hence it threatens transparency in the relationship. And as far as I know, transparency is one of the most important components in a relationship.
He'll Start Lying
As given example in the last point, not for watching porn but for everything else he'll start lying. Whenever you start to argue with him, he'll just accept your argument and ignore it later because he knows you don't accept his argument.
It'll lead to Break up
This might sound extreme but the breakup isn't a single step process. It happens gradually, step by tape while this is one of the dominant steps of it. More you manipulate him, more he'll talk to someone else ( friends or family) and hence he'll get lesser emotionally close to you and you know next.
Note: In this take, I've only used single gender-specific term him because it gets boring to read every time him/her but that doesn't mean this take is directed towards females only.
What Girls & Guys Said
1 1IF your relationship is strong you'll manipulate them by just having an opinion. If I said "I don't want you to go to university" two years back my girlfriend would ask why and it would have made her think twice. Maybe she would have gone closer to home, maybe not at all. I'm not really sure. Instead I pushed her into it and now she's happier then ever.
Influence is inevitable in a good relationship. In a healthy one it'll always be positive.
Yeah, it didn't end well for Scarlett Johansson in Don Jon.