Sanskrit was designed for sound. For millenia the profound teachings of India have been chanted over and over, preserving the essence of their meaning. Chanting Sanskrit forms a direct link to the vibrations of ancient India through sound. Many other cultures have preserved their texts through chanting as well.
In order to chant properly, it is paramount to pronounce correctly the Sanskrit words. When we say a Sanskrit word as if it were English, we miss the true vibration of whatever energy that word represents. This is especially true for chanting mantras, since they are recited hundreds and thousands of times in order to produce a particular effect. If the pronunciation is not accurate, then the effect of the sound, instead of enhancing, will divert the energy of the intention and focus. How would it sound if someone who did not know how to pronounce Italian for example, sang a song in Italian? Unfortunately this is the case in our Western culture around Sanskrit. There are many recordings of devoted, well-intentioned, highly talented singers who are pronouncing Sanskrit chants as if they were English.
I liked Nicolai's style of teaching -- he made Sanskrit easier to understand and has a very nice way of explaining the sutras and other components of yogic philosophy.