When I was a med student, I never got it when attendings said that med students ate up more time than they save. I mean, at best, I was like a little slave, fetching information, vital signs, and sometimes beverages. At worse, I was a silent shadow.
But now, as an attending, I totally get it.
When you have a student, unless you're a total ass, you have to teach them. And that takes up time.
Plus, let's face it, you can't cut corners as much when someone is observing you.
And finally, they're rarely helpful. Even when they think they're being helpful, like when they just spent over 2 hours writing up an H&P. Because I could have done the same damn thing in like 10 minutes.