Are greetings and salutations redundant in an e-mail?

Stack Exchange: "Some people might say the greeting and salutation are there for politeness. Is this really true? Will you be offended if they're left out? As a website user interface designer, I was always taught by the great usability experts (Steve Krug, Jacob Nielson) that writing more than you need is disrespectful of a website user's time. To me, leaving out the greeting and salutation makes the email easier to read.