Master of suspense Alfred Hitchcock gave an interview in 1973 in which he succinctly explained the difference between using suspense versus shock as an element in filmmaking. He said he preferred suspense, and used it "to convey, visually, certain elements in storytelling that transfers itself to the mind of the audience."
He said other filmmakers used visuals that were "purely objective. That's why you see a lot of blood on the screen. There's no subtlety about it because you present it to the audience in the visual form, and that's it!"
"I prefer to suggest something and let the audience figure it out," he said. "The big difference between suspense and shock, or surprise, is that in order to get suspense you provide the audience with a certain amount of information and leave the rest of it to their own imagination."
Via Laughing Squid