We need self-control in order to develop the healthy self and relationships. Self-control makes us be able to change behavior patterns because we think thats wrong.
In order to develop a healthy self, one must develop a strong sense of self-control to have sharper insight and a stronger will to set boundaries and limitations for their self. Self-control will protect one from complicated situations that could lead to harm physically, sociology, and mentally.
Not having self-control can cause anxiety and stress, which is bad for your health.
The disposition to control the self enables one to have control when associated to others, like in a relationship. The ability to take control over the self can be delayed because of some objectionable experiences in the past.
For example: if you were in a relationship with a guy/girl that cheated on you due to your lack of self control you might assume that your new boyfriend/girlfriend will do that to you, or you might not want your boyfriend/girlfriend talking to or interacting with the oppose sex
Also if you don't have self-control you can say things and do things you didn't mean which can cause a break up in any relationship