Tighter writing is clearer, and thus easier to read. If you can trim, you should be doing it anyway; leaving the extra amounts to cruft in most cases.
Effective visual communication, whether it be anything from body of text to an icon, is not necessarily contingent upon its complexity.
(And by long-form, I assume you are talking about an article or something rather than a book.) If you aren't concerned with people actually reading your text then yes, thats probably a good idea. But prefacing in this manner generally tends to disuade meaningful consumption, "why read in 4 pages what was summed up in 4 sentences", a reader might think. I think prefacing could arguably contribute to effective communication, but it stifles engagement significantly.
Just my 2 cents...