It is very important to know what mantra represents. Without a correct understanding of mantra, no matter how many times one recites the mantra, it can only alleviate negative karma caused by unwholesome words, but not gain any accomplishment. However, with the aforementioned right view, the effectiveness of applying mantra recitation to reduce negative karma, increase merit, and attain realization will be very different.

~ Depicted from GATEWAY TO VAJRAYANA PATH - The Generation Stage