I always wondered that when going for taraweeh or performing it myself...Here is what helped me decide.
Abu Dharr (ra) narrated, the Messenger of Allah (saw) said to me: “If you learn one ayah from the Book of Allah it is better for you than to voluntarily pray one hundred rakahs”
Anas relates that the Prophet (May Allah shower peace & blessings on him) said: ''a single person who understands the relegion has more virtue in Allah's court than a thousand worshippers.''
Abu Dharr & Abu Hurayrah said: ''Learning a chapter of knowledge is better than a thousand rakah's of nafl prayer, and pursuing a chapter of knowledge whether it be put into practice or not, is better than a hundred nafl rakahs.''
http://quran-tafsir.org/