This is actually kind of a bad thing to do, since you're intentionally wasting other people's time.
Why wouldn't you do the same with companies?
It's fine to interview at multiple companies that you might consider taking an offer from, but interviewing at a place you know you'll say no to strikes me as, yes, wasting their time (and money, as we usually have a few people interviewing one candidate at the same time).
No reason to feel bad about it especially if it is a big corp. These days employers throw careers under the bus at the whim of asshole mba's. And, no, employer's won't agree to "informational interviews" any more.
In any case no one has to know except the interviewee.