Here's a page full of reasons. I'll spare you the footnotes, but each reason is fully upheld by evidence from Vedic writings like Bhagavad-gita, the Upanisads, and the Puranas.
CHANTING HARE KRSNA awakens love of God.
Chanting Hare Krsna brings liberation as a side benefit along the way.
When you chant Hare Krsna, you automatically develop knowledge and detachment.
Chanting Hare Krsna gets you out of the endless cycle of birth and death.
It is the most effective means of self-realization in the present Age of Quarrel. Nothing else works nearly as well.
Chanting Hare Krsna cleanses the heart of all illusions and misunderstandings.
By chanting Hare Krsna, you become free from all anxieties.
Chanting Hare Krsna brings you to self-realization and shows you how to act as a self-realized soul.
It keeps you ever mindful of Krsna, the reservoir of pleasure.
There are no hard and fast rules for chanting. You can chant anywhere, any time, under any circumstances.
Krsna Himself is fully present in the transcendental sound of His name. And the more you chant, the more you realize it.
All other Vedic mantras are included in the chanting of Hare Krsna. So just by chanting this mantra, you get the benefit of all others.
Chanting Hare Krsna purifies not only you but every living entity around you. Whoever hears the chanting gets spiritual benefit.
A person who chants Hare Krsna develops all good qualities.
You can chant Hare Krsna softly for personal meditation or loudly with your family or friends. Both ways work.
Srila Prabhupada chanted Hare Krsna, and so did great souls in the past. So why not you? It's free. Chanting Hare Krsna never costs you money.
Chanting Hare Krsna brings the highest states of ecstasy.
There are no previous qualifications needed for chanting Hare Krsna. Young or old, anyone can chant from any race, any religion, or any country of the world.
Even if you don't understand the language of the mantra, it works anyway.
Chanting Hare Krsna brings relief from all miseries.
Chanting Hare Krsna is easy. When the best way is also the easiest, why make life hard for yourself?
Chanting Hare Krsna invokes spiritual peace for you and for those around you.
When you chant Hare Krsna, Krsna Himself becomes pleased.
When you chant Hare Krsna, Krsna dances on your tongue.
By chanting Hare Krsna you can return to Krsna's world, the eternal abode of full happiness and knowledge.
Chanting Hare Krsna frees you from the reactions of all past karma. Chanting Krsna's name even once, purely and sincerely, can free you from the reactions of more karma than you could possibly incur.
Chanting Hare Krsna counteracts the sinful atmosphere of Kali-yuga, the present Age of Hypocrisy and Quarrel.
By chanting Hare Krsna you can relish at every step the full nectar that's the real thirst of the soul.
The more you chant Hare Krsna, the better it gets.
If you look through all the Vedic scriptures, you'll find nothing higher than the chanting of Hare Krsna. Hare Krsna, Hare Krsna, Krsna Krsna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare.
– Jayadvaita Swami