Given the time period, the sound quality is quite good for a live album.
Listen to the audience. You often wouldn't know it is a live album. The audiences are like classical music audiences. They know when to shut up and LISTEN!
As for the music itself...Yes!! Yes seem to put a lot more energy into the live performances than is heard on the original studio recordings of these tracks.
Despite many more live versions and studio remakes, Yessongs contains the ultimate recordings of many classic Yes compositions from The Yes Album (1971), Fragile (1971), and Close to the Edge (1972).