The Lavaliere Mic
The third type of mic is the lavaliere mic (commonly called a "lapel mic" because it's often clipped to your jacket lapel). The lavaliere mic has several advantages ― it's easy to use, and it frees up both of your hands for you to use for other things (such as gestures). But as you'd expect, the lavaliere mic also has its own disadvantages.
Because you can't move it (once it's attached to your clothing, it isn't going anywhere), it's impossible for it to move when your mouth moves. This normally isn't a problem when you move your head from side to side (and fortunately, that's the most common movement). But if you look down when you speak, your voice will possibly "boom" when your mouth comes closer to the mic. And if you look upward toward the ceiling, the problem is worse ― the mic may not be able to pick up your voice at all.
Fortunately, people generally do not look up or down all that much in a presentation, so it may not be a problem for you. But you should be aware of that possibility so you don't let it happen.
Another problem with the lavaliere mic is that it's extra-sensitive to any sounds that are closer than your mouth. For instance, don't pound your chest Tarzan-style when you're wearing a lavaliere mic. Even a small thump will possibly generate a big BOOM that can startle both you and your audience.
And if you're wearing clothing that "rustles" when it moves (such as a loose-hanging scarf or lacy fabric), the rustling will be amplified by a lavaliere mic. And if you're wearing a necklace, be sure that it doesn't come anywhere near the mic ― the mic will pick up the slightest tinkle and amplify it into a distracting jangle.
Perhaps the worst problem of all, you need some place to clip the lavaliere mic. So if you're wearing a turtleneck sweater, for example, there may not be anyplace in front to clip the mic. (In such as case, probably the best thing to do would be to tape the mic to the side of your head, somewhat like a headset mic. Unfortunately, this can be distracting both to your audience and (especially) to you, so the best thing is to anticipate if you're going to be using a lavaliere mic and dress accordingly!)