It depends. If you're asking to be referred to someone, or introduced, you may want to try and understand the dynamics in a particular situation.
There is a lot of power for the recipient of the right referral - a chance to get the attention of a potential investor or advisor and to penetrate the normal screening mechanism.
If I'm doing the referring it carries my implied endorsement of the person and venture being referred. Because I value the relationship with people I know, I most probably will add some color to the "why" and explain what I think the benefit might be.
For instance, I've recently written "Bill, I'd like you to consider talking to Ned at Newco who has an intriguing start up that's made some traction in the party planning/social media space as evidenced by some good stats on customer sign-up and early salres results. We aren't looking at SM deals right now as we're busy with what we re in, but I know you re in this space and suggest you take a look. I'm attaching a deck. Let me know if this is interesting to you and/or if you wnt to talk about it."
It's clear that I am making this referral because I think it may have value for Bill - a friend of mine - and will be good for Ned as well.
I consider introductions to imply less commitment, as in "Sally, meet Joe Smith who would like to talk to you. He asked if I knew you, and, having recently met him through Milwaukee Talks, I was glad to send this note."
In this second case, it's clear to both parties that I am taking less responsibility for the contact - and am saying so.
A third way this happens for me is that if I'm talking to someone about ideas, plans or goals, and I think they are credible, I'll often proactively suggest people they should meet - and I'll tell them why. Our group recently reviewed a plan that included a couple of high powered and very competent advisors - and those advisors got to the opportunity because I'd suggested - years ago - that the entrepreneur talk to them.
All of this stuff is a virtuous cycle that enlarges opportunity for everyone - to meet new people, think about new ideas, put things together.
So what is the "depends" part?
It's called "passing the buck." If you feel you've been passed on to someone just to get you off the phone or some other similarly inappropriate reason, you've learned a lot about the character of the person.
I think it's perfectly fair to politely ask a little about why the person referring you thinks this is a good idea and what it might do to help you.
And, of course, be prompt in your followup.