It is a strong belief that chanting the Om in the basic purest form kills or greatly reduces Kaam Vasna [sexual desire or lust], which is an essential part of Grihasthashram and Grihasthashram, cannot be complete without Sexual desire. As already mentioned in many earlier posts, true Hinduism does not frown upon the topic of sex nor does it consider it taboo.
Hindu Rishis, Sages and those on the road of spiritual discovery mediate upon the Om for spiritual evolution, as this purest basic sound is the key to open the doors of higher and higher planes of existence. One of the major obstacles in spiritual evolution and entering the golden silence is sexual lust and Om along with its infinite attributes frees the seeker from this lust.
For householders the Om is chanted along with a mantra to increase its strength and potency like in Om Namo Shivaya ॐ नमो शिवाय or Om Gam Ganapataye Namah ॐ गं गणपतये नमः or for that matter in any of the other Hindu Vedic and Shabar Mantras.
However, those householders who have no interest in Kaam Vasna, like elderly people can chant the basic Om as it is extremely potent and powerful not only in bringing about spiritual growth and evolution, but also in reducing physical problems and energizing the body.