To me, shorter sentences are great for punctuating a point, but they can really lack depth at times. The other day, on another post, I mentioned a sentence I had to study in detail in college that my instructor held as the greatest sentence he was aware of (I learned a great deal from studying it).
Shreve was coming up the walk, shambling, fatly earnest, his glasses glinting beneath the running leaves like little pools.
This sentence, while not overly long, has seemingly infinite depth; it would be impossible to recreate its appeal with several sentences that purport to convey the same information. Each modifying clause adds another layer to the initial, simple sentence, and each clause is even successively more complex, the first being plain vanilla, the second inventing a new word (fatly), so that we may envision in our heads what Faulkner even means by "fatly earnest", a phrase that none of us has ever heard, but that we can intuit immediately, the final using a very delicate metaphor, beautiful yet precise. Simplicity just would not do. Anyway, I guess my point is that variety is the most important thing. One needs to know when to use subtle, complex sentences, and when to use the blunt force of a short sentence.