This is beyond "required listening". Two legends; one at the apex of his career, one at the nadir. Zappa was selling out arenas and Beefheart couldn't get anyone to play with him (the entire Magic Band up and quit on him in '74, due to his "abusive behavior"). Needless to say, Beefheart couldn't get a gig at a dive bar and Frank felt he owed him (they've been friends since high school). The two geniuses had a pretty strained relationship around this time; they were both on "ego trips" says former Zappa drummer Jimmy Carl Black, with Beef mostly drawing sketches on-stage of Zappa and Frank in turn hating the Captain's work ethic (Zappa was a notorious workhorse).
This album is notable also for the lineup featured; it's at the intersection of two of Frank's greatest bands- blending the early 70's incarnation with Napoleon Murphy Brock and Chester Thompson with the late 70's era band with Terry Bozzio and the Fowler brothers.
One of my favorite records of the mid-1970s; listen to the Captain ramble nonsense over fantastic Zappa art rock compositions. Enjoy!