Let me just say that I have people hitting me up all the time for advertising, traffic, etc. etc.
I deal specifically with sales, so while I can offer advice and suggestions on those things, inevitably they need to speak with someone else to get what they're after.
I'd assume most people don't want their time wasted and would rather talk to the person who can help them directly, so I'm gonna send them there.
Now, if I can't help them when it comes to what MY job is, then yes, I'm useless.
However, something to keep in mind is in a large company, it's sometimes necessary to "Go through channels" to get a definitive answer.
edit-when it's something I can RELAY to the person and find out FOR them, I'll do that too, because then I've learned something that will help me in the future as well.