You can have a world-class director, a cast of talented A-list stars and a catering team so on point they deserve a Michelin star, but if a film doesn't have a good editor then all that effort's for naught. Until that skilled individual is wrangling all the various takes of every scene, normally shot completely out of order, and stringing them together into a concise, but still coherent, feature, nobody knows if they're heading to the Oscars or the Razzies.
One of the most important things an editor does is brutally cutscenes. It's always a shame to see hard work (and money) go to waste, but it really is worth it at the sake of a movie's length. There are, after all, few things worse than a movie that's too long (imagine how slightly more bearable Michael Bay's Transformers would have been if they'd only been ninety minutes long apiece).
But it's not just due to time constraints that the DVD gets its deleted scenes special feature; sometimes there's moments that would have actively ruined a film if they hadn't been removed. Take these eight scenes. They're deceptively short, running only about a minute each, and yet would have completely uprooted their respective movies had they been included, providing resolution to delightfully ambiguous endings or painting characters in a totally different light.