For a huge percentage of people involved in body modification, at least a part of the motivation is sexual pleasure.
That said, there is a great deal of disagreement as to what feels good, what feels the same, and, in some cases, what feels worse. Some people LOVE the feeling of genital beads, or an apadravya, or think that tongue piercings enhance oral sex. But just as many people really can't tell the difference.
If you are in touch with yourself, and with your partner, body modifications can dramatically enhance your sex life.