Here's someone who claims that the elevator pitch is an irrelevant exercise:
And here are two "pro-elevator-pitch articles" that tell you how and why to craft such a pitch:
So which side am I on? Well... both.
The first item (on Fortune and CNN Money's website--impressive sources) speaks against such canned speeches as potentially doing more harm than good, by sucking up all the air in the elevator. Yeah; I don't think you should corner people when they can't walk away from you and blat out an abbreviated LinkedIn profile without taking a breath even once.
But the second item (Bloomberg Business Week, another impressive source) lists as its first "how-to" heading "Keep it fresh." Exactly. You can't possibly prepare for every situation where you might have a chance to sell yourself, tacitly or even more directly. As the Fortune blog post points out, what you're after is a conversation, not a monologue.
And if you look at the MindTools website's step-by-step instructions, you'll see that the exercise of crafting an elevator speech can get you thinking about important parts of what you have to offer an employer. In fact, if you haven't thought hard about each of these steps--what you want, what an employer will find valuable about you--I might argue that you aren't ready for the job market yet.
Drafting an elevator speech is something like taking a test in college. You study, study, study for many hours, and then sit down to take an exam that lasts all of an hour or so. Why did you study for hours, instead of studying only the stuff that was actually on the exam? Because no exam can truly measure all you should have learned--it can only sample. You learn it all so you can present the right samples to demonstrate you've mastered the whole.
Just so, no employer can use all the intelligence and skills you possess; but you'd jolly well better be able to highlight the ones a prospective employer would be interested when that opportunity rolls around.