Vary sentence length, structure, etc., for lively prose is practical and helpful advice. However, I've yet to see, read, or hear pragmatic advice on more than a simple why or two to vary sentence structure, like because -- for poetic rhythm and song and so sameness doesn't dull readers -- let alone writing in the first place.
Why else? How? When? What? You know, the six W questions nuanced to helpful degrees. Timely and judicious emphasis is a central function. Beyond that, possibles reach toward infinity. Short sentences, faster pace; long sentences, at times slower, at times faster pace. Varied sentence length can in and of itself create a movement arc. One syntax essential is unity of idea -- too often too much idea jammed into a clause, sentence, paragraph, and longer syntax unit.