One will delight in remembering H'shem when alone and feel empty when not reflecting on His greatness. Even in great assemblies of people, he will desire only to please Him and will long to meet only Him. pg 469,471
Daily Halacha Teves 26
From a halachic point of view, it is important to distinguish between those portions of the davening in which talking is prohibited because o hefsek ( Birchos Kerias Shem and Shema Shemoneh Esreh Kedushah, Hallel) where not even a single word is permitted to be uttered regardless of "need" and those portions where the prohibition against talking is based on the requirement of paying attention to the davening or because of shul decorum (e.g., Kaddis chazaras ha-shatz) where an exception can be made when a special need arises allowing one to quietly utter a few words. The following statement authored by Harva Shimon Schwarb sums up the Torah viewpoint on the subject:
"For H'shem's sake, let us be quiet in the Beis ha-Knesses. Our reverent silence during the Tefillah will speak very loudly to Him, Who holds our fate in His hands. Communicating with H'shem is our only recourse in this era of trial and tabulation. There is too much ugly noise in our world today. Let us find peace and tranquility while we stand before Hashem in prayer.