Many web conferencing vendors allow you to display a live image of presenters on the audience's console during a webinar. Cute technology. Don't do it.
Okay, gauntlet flung. Now I can dig in to the topic a bit. Sure, you can use this feature if you are having an interdepartmental brainstorming session or business meeting with people you know. But don't use it for general webcasting of investor relations calls, marketing pitches, or introductory business sessions.
The short reason why can be summed up in a single well-known example. The 1960 Nixon vs. Kennedy presidential debates. For the whippersnappers in our audience who don't know the story, read this short summary. It's important and it won't take you much time. People who listened on radio came away with the impression that Nixon had clearly won the debate. 70 million television viewers said exactly the opposite.
When you video broadcast your talking head, are you ready to set up proper lighting? Use makeup to cover small blemishes and reduce glare? Create a professional non-distracting background? Keep the camera angle perfectly aligned so it doesn't shoot into your nostrils or off your gleaming forehead? Stay dead still so you don't move out of frame, out of focus, or weave back and forth giving your audience vertigo? Keep from blinking your eyes too much? If you think any of these items is trivial or shouldn't matter, you aren't ready to use video as a professional tool.
Let's say you do all of those things (and for all practical purposes, you CAN'T... not without a professional studio and experienced technicians). You now have to worry about how you look with your headset on or your phone held to your ear. Fairly silly is the answer. Then you are probably going to see your own image on the monitor. For some reason, most of the vendors don't have a way to turn this off for the speaker. Bad idea... you will start focusing on your image, trying to center your head and moving the wrong way, and losing track of your topic. (Tip: If you find yourself backed into a corner with this problem, use a post-it note to cover the image on the screen so you can't see yourself.)
Now we move to the ways that various vendors deal with multiple presenters for a webcast. Some use "follow the speaker" technology that automatically presents the head of the current speaker. If you get into a Q&A session with multiple comments, the image can flip between people so much that it causes nausea. Some vendors use multiple heads all presented in a row. This always reminds me of early music videos by the rock group Queen. An itty bitty corner of a computer monitor is no place for multiple talking heads.
The chief argument in favor of the talking heads (I know... I know... "Is that they have really great music." Just let the joke go.) is that your audience is more interested and involved when they can see who is speaking. This is literally true. Just not in the way you want. They are interested in poring over details of your face, your office, and your expressions and they are involved in deciding whether you look trustworthy or too young or too old or like their first boyfriend or something. They are NOT interested and involved in your subject material anymore.
If you feel you need video for your web conference, spend the money and book a professional video studio with professional cameramen. Otherwise leave off the video. Webcams are toys, not business tools.