Abstinence is all about the practice of restraint. It is about controlling one’s self, usually from an addictive substance (such as alcohol), though in some quarters, it is also regarding as a form of birth control.
Restraining one’s self from bad habits is no bad thing. In some regards, vegetarians are practicing abstinence from meat. I know a few vegetarians who would love to sink their teeth into a crisp bacon sandwich, but for all their fond memories of meat, they hold back. That’s commendable.
In some cases, abstinence can be regarded as denying something for the wrong reason. Denial of the sexual reality of human relationships and instincts is a good example. Some people ignorantly regard abstinence as effective birth control; it is effective for as long as people actually practice it, but sex is an integral part of a healthy, loving relationship, and the failure to properly education young people on contraception means unwanted pregnancies. The fact is, couples – especially young, new couples – will always be looking to have sex, and if sex is not stigmatised, or made to seem like a dirty act, and if genuine education and contraceptive options exist, that will always be preferable to the emotionally/romantically stunting (not to mention inevitably failing) practice of abstinence.