This is a simple mantra for your speeches. Your presentation or speech, regardless of how big of an audience you are giving it to, should be important enough that people will want to be there and get something out of it. If people are sitting there asking themselves "Why am I here?" then you need to work on your speeches.
The problem with a lot of speeches that I hear is that I am asking myself that question a lot of times. Many times the speaker is droning on about something that I don't need or they are reading their slides to you. They do this even after they have given you their handouts with their slides on it. Which means I've flipped through the slides, read all the material and yet I have to sit here for another 30 minutes while you read all of your slides!
So please, take a cue from myself and Seth Godin - when you are preparring your speeches ask yourself "Are people getting something out of this speech or are they asking themselves - why am I here?" This simple guideline can help you with your speeches. Make sure that you cut out information that you don't need and make sure you are giving a speech that people are going to want to be present at.