It allows you to relax and to get into a meditative trance. So that you can get into touch with yourself. You will be able to connect to your higher power. Now Doctor's are say this is something that each of us should do because it can extend our lives.
Meditiation needs not be etched in stone. This is because when one meditates, there are those that find it easy, and those that find it hard. The repetition and methodic nature may be a "level 1", like an infant or child learning to speak. "Level 2" may be the ability to reach the subconscious.
Repetitive chants help increase meditative states. Focusing on such things like breathing or the same sounds over and over help let minds wander and drift into nothingness. That nothingness is where the meditative state comes from. In that emptiness, the mind can be filled with whatever messages it needs from the universe.
Yes, I find chants such as the Hare Krishna mantra to be meditative, because they have a musical component to them that are entrancing. Hare Krishna has a ring to it, and it draws people in. Because it attracts the listener and distracts them, it is not just repetitive and methodical, but it has a meditative component to it.
I do not find the Hare Krishna mantra to be useful in meditation. I have tried it several times and have found that it is more a nuisance than anything else. In fact, for me, repeating a mantra tends to make me focus more on the mantra itself, making it a complete distraction. It becomes repetitive but that's about all it does.