From Carrie Rickey at The Philadelphia Inquirer:
Before Dede Allen, the sound you heard matched the image on the screen. But when Allen spliced The Hustler (1961), locating the psychology of each scene in the establishing shot (the ambitious glint in Paul Newman's eye, the collision of balls on the pool table to indicate the collision of wills between "Fast Eddie" Felson and his rival Minnesota Fats) and overlapping the sound from the forthcoming scene as a segue between sequences, everything changed. Allen didn't think editing should be codified like a textbook but rather allusive like a poem. (Her mentor, Robert Wise - the film editor on Citizen Kane, who hired her to cut his Odds Against Tomorrow - is said to have encouraged her experimentation.)
Dede Allen also edited the free-form, counter-culture masterpiece Alice's Restaurant (1969), hard-nosed Serpico (1973), Dog Day Afternoon (1978), Warren Beatty's epic Reds (1981) and even the Gen X touchstone The Breakfast Club (1985).
As Felicia Lee noted in The New York Times, Allen "revolutionized images with a staccato style that gave a story a sense of constant motion."
In other words, Allen is -- for all intents and purposes -- the mother of modern film editing. If you love how the films of the late 1960s, 1970s, and 1980s "move" and "speak" (how they visually express their narratives), then you have Dede Allen to thank for it. Allen will be missed, but her talent will never be forgotten, not so long as film history is remembered, debated and cherished.